Added environment variable for base container
Added environment variable for base container

In order to be able to use a different base image i have added another
environment variable where everybody can switch the used base container
for the applications directly through the environment variable
DOKKU_IMAGE or with the help of the dokkurc configuration.

ddreaml/dokku,vlipco/dokku,basicer/dokku,Evlos/dokku,fmoliveira/dokku,expa/dokku,beni55/dokku,leonardodino/dokku,pmvieira/dokku,frog/dokku,rocLv/dokku,AnselZhangGit/dokku,bkniffler/dokku,cjblomqvist/dokku,mehulsbhatt/dokku-alt,callahad/dokku,Git-Host/dokku,dokku/dokku,stepri/dokku,tilgovi/dokku,akatrevorjay/dokku,biddyweb/dokku,ebeigarts/dokku,beedesk/dokku,beni55/dokku,jimeh/dokku,beni55/dokku,econya/dokku,lmars/dokku,davidsiefert/dokku,vkurup/dokku,hanwoody/dokku,suxor42/dokku,basicer/dokku,barseghyanartur/dokku,dsrowell/dokku-alt,amaltson/dokku,jamesblunt/dokku,jimjag/dokku,alexquick/dokku,progrium/dokku,dokku-alt/dokku-alt,progrium/dokku,callahad/dokku,progrium/dokku,expa/dokku,jazzzz/dokku,omeid/dokku,elia/dokku,mehulsbhatt/dokku-alt,Evlos/dokku,stepri/dokku,eljojo/dokku,henrik/dokku,vkurup/dokku,vfulco/dokku-alt,stnly/dokku-alt,dokku/dokku,johnfraney/dokku,suxor42/dokku,vijayviji/dokku,dokku/dokku,TribeMedia/dokku,progrium/dokku,beedesk/dokku-alt,stepri/dokku,gianpaj/dokku,progrium/dokku,mouserage/dokku,bobvanderlinden/dokku,kennetham/dokku,ertrzyiks/dokku,emdantrim/dokku,ertrzyiks/dokku,stnly/dokku-alt,Fab-IT-ApS/dokku,claytonbrown/dokku,vlipco/dokku,lmars/dokku,arthurschreiber/dokku,biddyweb/dokku,suxor42/dokku,beni55/dokku,Cactusbone/dokku,rocLv/dokku,alexquick/dokku,ddreaml/dokku,stnly/dokku-alt,vlipco/dokku,cjblomqvist/dokku,davidsiefert/dokku,netbrick/dokku-alt,experimental-platform/dokku,vijayviji/dokku,jamesblunt/dokku,dokku-alt/dokku-alt,basicer/dokku,ertrzyiks/dokku,fruitl00p/dokku,davidsiefert/dokku,3onyc/dokku,kennetham/dokku,akatrevorjay/dokku,fmoliveira/dokku,mmerickel/dokku,barseghyanartur/dokku,ddreaml/dokku,arthurschreiber/dokku,claytonbrown/dokku,henrik/dokku,Cactusbone/dokku,alessio/dokku,bkniffler/dokku,johnfraney/dokku,vijayviji/dokku,Evlos/dokku,sebastianscatularo/dokku,ertrzyiks/dokku,mmerickel/dokku,sebastianscatularo/dokku,dokku/dokku,rocLv/dokku,Git-Host/dokku,netbrick/dokku,stepri/dokku,codeconfab/dokku,lmars/dokku,beedesk/dokku-alt,progrium/dokku,AnselZhangGit/dokku,mouserage/dokku,matto1990/dokku,leonardodino/dokku,jamesmarva/dokku,basicer/dokku,jazzzz/dokku,matto1990/dokku,crisward/dokku,bewest/dokku-alt,mouserage/dokku,arsthanea/dokku,beni55/dokku,emdantrim/dokku,beni55/dokku,crisward/dokku,leonardodino/dokku,kennetham/dokku,sseemayer/dokku,arthurschreiber/dokku,frog/dokku,netbrick/dokku,jimeh/dokku,akatrevorjay/dokku,dokku-alt/dokku-alt,netbrick/dokku-alt,experimental-platform/dokku,jamesmarva/dokku,callahad/dokku,mrluc/dokku,ddreaml/dokku,kennetham/dokku,hanwoody/dokku,pmvieira/dokku,arsthanea/dokku,elia/dokku,dokku-alt/dokku-alt,leonardodino/dokku,omeid/dokku,fmoliveira/dokku,sebastianscatularo/dokku,stnly/dokku-alt,paralin/crew,biddyweb/dokku,fruitl00p/dokku,vijayviji/dokku,sseemayer/dokku,Cactusbone/dokku,Evlos/dokku,mehulsbhatt/dokku-alt,kennetham/dokku,jamesmarva/dokku,jazzzz/dokku,netbrick/dokku-alt,mmerickel/dokku,paralin/crew,arthurschreiber/dokku,mehulsbhatt/dokku-alt,dokku-alt/dokku-alt,beedesk/dokku,3onyc/dokku,basicer/dokku,Evlos/dokku,tilgovi/dokku,claytonbrown/dokku,3onyc/dokku,basicer/dokku,matto1990/dokku,experimental-platform/dokku,klodoo/dokku,beedesk/dokku,matto1990/dokku,eljojo/dokku,fmoliveira/dokku,hanwoody/dokku,suxor42/dokku,alexquick/dokku,dsrowell/dokku-alt,cjblomqvist/dokku,gianpaj/dokku,basicer/dokku,omeid/dokku,jimjag/dokku,econya/dokku,davidsiefert/dokku,arsthanea/dokku,progrium/dokku,suxor42/dokku,jamesmarva/dokku,henrik/dokku,davidsiefert/dokku,Git-Host/dokku,AnselZhangGit/dokku,vijayviji/dokku,frog/dokku,netbrick/dokku-alt,ebeigarts/dokku,stepri/dokku,u2mejc/dokku,alessio/dokku,arsthanea/dokku,mmerickel/dokku,eljojo/dokku,klodoo/dokku,klodoo/dokku,cjblomqvist/dokku,klodoo/dokku,eljojo/dokku,fruitl00p/dokku,cjblomqvist/dokku,netbrick/dokku-alt,callahad/dokku,biddyweb/dokku,klodoo/dokku,amaltson/dokku,3onyc/dokku,Fab-IT-ApS/dokku,callahad/dokku,gianpaj/dokku,jazzzz/dokku,netbrick/dokku,bkniffler/dokku,tilgovi/dokku,dsrowell/dokku-alt,lmars/dokku,bobvanderlinden/dokku,beedesk/dokku,netbrick/dokku,arthurschreiber/dokku,sebastianscatularo/dokku,vlipco/dokku,cjblomqvist/dokku,beni55/dokku,codeconfab/dokku,arthurschreiber/dokku,henrik/dokku,davidsiefert/dokku,elia/dokku,kennetham/dokku,vlipco/dokku,crisward/dokku,mouserage/dokku,Cactusbone/dokku,omeid/dokku,Git-Host/dokku,fmoliveira/dokku,stnly/dokku-alt,amaltson/dokku,omeid/dokku,AnselZhangGit/dokku,stnly/dokku-alt,alessio/dokku,experimental-platform/dokku,vijayviji/dokku,codeconfab/dokku,fruitl00p/dokku,Fab-IT-ApS/dokku,pmvieira/dokku,barseghyanartur/dokku,barseghyanartur/dokku,econya/dokku,davidsiefert/dokku,jazzzz/dokku,bobvanderlinden/dokku,bewest/dokku-alt,bewest/dokku-alt,lmars/dokku,econya/dokku,netbrick/dokku-alt,arsthanea/dokku,ebeigarts/dokku,econya/dokku,ddreaml/dokku,dokku/dokku,Git-Host/dokku,vkurup/dokku,fmoliveira/dokku,eljojo/dokku,expa/dokku,beedesk/dokku-alt,pmvieira/dokku,fruitl00p/dokku,callahad/dokku,sseemayer/dokku,TribeMedia/dokku,sseemayer/dokku,lmars/dokku,mmerickel/dokku,bkniffler/dokku,amaltson/dokku,arsthanea/dokku,beedesk/dokku-alt,ebeigarts/dokku,3onyc/dokku,basicer/dokku,arthurschreiber/dokku,Evlos/dokku,vkurup/dokku,dokku-alt/dokku-alt,Cactusbone/dokku,netbrick/dokku,jazzzz/dokku,akatrevorjay/dokku,cjblomqvist/dokku,ebeigarts/dokku,Git-Host/dokku,alessio/dokku,crisward/dokku,mrluc/dokku,econya/dokku,fmoliveira/dokku,TribeMedia/dokku,dsrowell/dokku-alt,pmvieira/dokku,vijayviji/dokku,crisward/dokku,experimental-platform/dokku,emdantrim/dokku,u2mejc/dokku,pmvieira/dokku,crisward/dokku,u2mejc/dokku,bkniffler/dokku,mouserage/dokku,jamesblunt/dokku,tilgovi/dokku,klodoo/dokku,AnselZhangGit/dokku,ertrzyiks/dokku,arsthanea/dokku,elia/dokku,tilgovi/dokku,vkurup/dokku,jamesblunt/dokku,amaltson/dokku,omeid/dokku,claytonbrown/dokku,bobvanderlinden/dokku,stnly/dokku-alt,sebastianscatularo/dokku,amaltson/dokku,codeconfab/dokku,dsrowell/dokku-alt,beedesk/dokku,crisward/dokku,frog/dokku,lmars/dokku,jimeh/dokku,emdantrim/dokku,claytonbrown/dokku,leonardodino/dokku,omeid/dokku,omeid/dokku,ddreaml/dokku,akatrevorjay/dokku,jimjag/dokku,netbrick/dokku-alt,amaltson/dokku,fruitl00p/dokku,rocLv/dokku,dokku-alt/dokku-alt,TribeMedia/dokku,jazzzz/dokku,TribeMedia/dokku,vlipco/dokku,ebeigarts/dokku,cjblomqvist/dokku,3onyc/dokku,alessio/dokku,TribeMedia/dokku,dokku/dokku,gianpaj/dokku,Cactusbone/dokku,elia/dokku,expa/dokku,eljojo/dokku,vlipco/dokku,beedesk/dokku,barseghyanartur/dokku,jimeh/dokku,jimeh/dokku,mrluc/dokku,dsrowell/dokku-alt,mouserage/dokku,mrluc/dokku,alexquick/dokku,netbrick/dokku,jimjag/dokku,bkniffler/dokku,henrik/dokku,Evlos/dokku,dokku-alt/dokku-alt,ertrzyiks/dokku,codeconfab/dokku,frog/dokku,hanwoody/dokku,vkurup/dokku,jimjag/dokku,arthurschreiber/dokku,mrluc/dokku,tilgovi/dokku,TribeMedia/dokku,kennetham/dokku,davidsiefert/dokku,johnfraney/dokku,Evlos/dokku,elia/dokku,mehulsbhatt/dokku-alt,experimental-platform/dokku,johnfraney/dokku,Cactusbone/dokku,barseghyanartur/dokku,expa/dokku,Fab-IT-ApS/dokku,stepri/dokku,ddreaml/dokku,vfulco/dokku-alt,henrik/dokku,rocLv/dokku,jamesmarva/dokku,ddreaml/dokku,jamesblunt/dokku,fruitl00p/dokku,dokku/dokku,kennetham/dokku,beedesk/dokku,vkurup/dokku,akatrevorjay/dokku,jimjag/dokku,beni55/dokku,mrluc/dokku,u2mejc/dokku,jazzzz/dokku,beedesk/dokku,alexquick/dokku,matto1990/dokku,AnselZhangGit/dokku,hanwoody/dokku,expa/dokku,jamesmarva/dokku,henrik/dokku,sebastianscatularo/dokku,akatrevorjay/dokku,mehulsbhatt/dokku-alt,expa/dokku,3onyc/dokku,bobvanderlinden/dokku,eljojo/dokku,jamesblunt/dokku,matto1990/dokku,alessio/dokku,u2mejc/dokku,netbrick/dokku,alexquick/dokku,callahad/dokku,Git-Host/dokku,jimeh/dokku,dsrowell/dokku-alt,u2mejc/dokku,johnfraney/dokku,frog/dokku,mmerickel/dokku,barseghyanartur/dokku,netbrick/dokku-alt,ebeigarts/dokku,jimjag/dokku,rocLv/dokku,econya/dokku,Fab-IT-ApS/dokku,econya/dokku,codeconfab/dokku,beedesk/dokku-alt,TribeMedia/dokku,pmvieira/dokku,Fab-IT-ApS/dokku,vfulco/dokku-alt,leonardodino/dokku,tilgovi/dokku,alessio/dokku,emdantrim/dokku,suxor42/dokku,suxor42/dokku,beedesk/dokku-alt,amaltson/dokku,3onyc/dokku,bewest/dokku-alt,sseemayer/dokku,stnly/dokku-alt,stepri/dokku,frog/dokku,barseghyanartur/dokku,mouserage/dokku,bewest/dokku-alt,gianpaj/dokku,bobvanderlinden/dokku,johnfraney/dokku,sseemayer/dokku,emdantrim/dokku,sseemayer/dokku,dokku/dokku,alexquick/dokku,bewest/dokku-alt,gianpaj/dokku,vfulco/dokku-alt,vlipco/dokku,dsrowell/dokku-alt,bewest/dokku-alt,codeconfab/dokku,fruitl00p/dokku,stepri/dokku,bobvanderlinden/dokku,bkniffler/dokku,claytonbrown/dokku,vkurup/dokku,leonardodino/dokku,bewest/dokku-alt,sebastianscatularo/dokku,biddyweb/dokku,claytonbrown/dokku,suxor42/dokku,jimjag/dokku,Cactusbone/dokku,johnfraney/dokku,rocLv/dokku,pmvieira/dokku,vfulco/dokku-alt,netbrick/dokku,Git-Host/dokku,mrluc/dokku,alessio/dokku,callahad/dokku,jamesmarva/dokku,hanwoody/dokku,hanwoody/dokku,vfulco/dokku-alt,klodoo/dokku,beedesk/dokku-alt,mehulsbhatt/dokku-alt,henrik/dokku,experimental-platform/dokku,ertrzyiks/dokku,bobvanderlinden/dokku,jimeh/dokku,crisward/dokku,experimental-platform/dokku,gianpaj/dokku,elia/dokku,vijayviji/dokku,matto1990/dokku,emdantrim/dokku,biddyweb/dokku,claytonbrown/dokku,vfulco/dokku-alt,sebastianscatularo/dokku,AnselZhangGit/dokku,ertrzyiks/dokku,jimeh/dokku,johnfraney/dokku,lmars/dokku,emdantrim/dokku,bkniffler/dokku,expa/dokku,hanwoody/dokku,mmerickel/dokku,eljojo/dokku,AnselZhangGit/dokku,biddyweb/dokku,matto1990/dokku,arsthanea/dokku,jamesblunt/dokku,jamesmarva/dokku,codeconfab/dokku,progrium/dokku,gianpaj/dokku,Fab-IT-ApS/dokku,ebeigarts/dokku,u2mejc/dokku,klodoo/dokku,biddyweb/dokku,tilgovi/dokku,rocLv/dokku,mrluc/dokku,leonardodino/dokku,vfulco/dokku-alt,mehulsbhatt/dokku-alt,fmoliveira/dokku,elia/dokku,mouserage/dokku,akatrevorjay/dokku,beedesk/dokku-alt,mmerickel/dokku,sseemayer/dokku,alexquick/dokku,Fab-IT-ApS/dokku,u2mejc/dokku