Fix support for LDAP Authentication mechanism.
Fix support for LDAP Authentication mechanism.

This addresses a few issues:
* The LDAP authentication integration now creates an account a new
  Zulip account if the user authenticated correctly but didn't have a
  Zulip account.
* The previous code didn't correctly disable the LDAP group
  permissions functionality.  We're not using groups support from the
  Django LDAP extension and not doing so can cause errors trying to
  fetch data from LDAP.

Huge thanks to @toaomatis for the initial implementation of this.

Fixes #72.

christi3k/zulip,karamcnair/zulip,ryansnowboarder/zulip,cosmicAsymmetry/zulip,andersk/zulip,christi3k/zulip,grave-w-grave/zulip,isht3/zulip,rht/zulip,timabbott/zulip,JPJPJPOPOP/zulip,kou/zulip,vakila/zulip,dattatreya303/zulip,jrowan/zulip,jainayush975/zulip,j831/zulip,ahmadassaf/zulip,souravbadami/zulip,eeshangarg/zulip,jrowan/zulip,grave-w-grave/zulip,mohsenSy/zulip,sharmaeklavya2/zulip,Galexrt/zulip,Vallher/zulip,umkay/zulip,shubhamdhama/zulip,susansls/zulip,kou/zulip,KingxBanana/zulip,SmartPeople/zulip,blaze225/zulip,dattatreya303/zulip,timabbott/zulip,jainayush975/zulip,alliejones/zulip,kou/zulip,Frouk/zulip,vabs22/zulip,souravbadami/zulip,zacps/zulip,ashwinirudrappa/zulip,jainayush975/zulip,vakila/zulip,atomic-labs/zulip,ahmadassaf/zulip,zulip/zulip,peiwei/zulip,mohsenSy/zulip,vabs22/zulip,aakash-cr7/zulip,rishig/zulip,zacps/zulip,verma-varsha/zulip,peiwei/zulip,sup95/zulip,amyliu345/zulip,amanharitsh123/zulip,vakila/zulip,jackrzhang/zulip,timabbott/zulip,calvinleenyc/zulip,sup95/zulip,sharmaeklavya2/zulip,tommyip/zulip,peguin40/zulip,ahmadassaf/zulip,jrowan/zulip,rishig/zulip,ryansnowboarder/zulip,paxapy/zulip,peguin40/zulip,TigorC/zulip,jainayush975/zulip,KingxBanana/zulip,KingxBanana/zulip,susansls/zulip,zulip/zulip,Jianchun1/zulip,ashwinirudrappa/zulip,punchagan/zulip,AZtheAsian/zulip,cosmicAsymmetry/zulip,hackerkid/zulip,ashwinirudrappa/zulip,susansls/zulip,umkay/zulip,brainwane/zulip,dattatreya303/zulip,joyhchen/zulip,jackrzhang/zulip,dhcrzf/zulip,showell/zulip,eeshangarg/zulip,reyha/zulip,vabs22/zulip,krtkmj/zulip,dawran6/zulip,verma-varsha/zulip,joyhchen/zulip,jphilipsen05/zulip,grave-w-grave/zulip,mahim97/zulip,Diptanshu8/zulip,tommyip/zulip,Jianchun1/zulip,sonali0901/zulip,christi3k/zulip,gkotian/zulip,synicalsyntax/zulip,joyhchen/zulip,Vallher/zulip,TigorC/zulip,Galexrt/zulip,ashwinirudrappa/zulip,ryanbackman/zulip,alliejones/zulip,sharmaeklavya2/zulip,j831/zulip,tommyip/zulip,brainwane/zulip,PhilSk/zulip,karamcnair/zulip,blaze225/zulip,mohsenSy/zulip,ahmadassaf/zulip,dwrpayne/zulip,SmartPeople/zulip,verma-varsha/zulip,esander91/zulip,rht/zulip,jackrzhang/zulip,Galexrt/zulip,vikas-parashar/zulip,karamcnair/zulip,reyha/zulip,mahim97/zulip,umkay/zulip,verma-varsha/zulip,vakila/zulip,dwrpayne/zulip,Jianchun1/zulip,zulip/zulip,cosmicAsymmetry/zulip,aakash-cr7/zulip,ashwinirudrappa/zulip,niftynei/zulip,ryanbackman/zulip,souravbadami/zulip,krtkmj/zulip,Juanvulcano/zulip,isht3/zulip,kou/zulip,PhilSk/zulip,hackerkid/zulip,dattatreya303/zulip,eeshangarg/zulip,SmartPeople/zulip,grave-w-grave/zulip,vakila/zulip,samatdav/zulip,alliejones/zulip,rishig/zulip,paxapy/zulip,umkay/zulip,cosmicAsymmetry/zulip,umkay/zulip,umkay/zulip,calvinleenyc/zulip,karamcnair/zulip,samatdav/zulip,ryanbackman/zulip,showell/zulip,punchagan/zulip,paxapy/zulip,dwrpayne/zulip,Diptanshu8/zulip,amanharitsh123/zulip,reyha/zulip,dwrpayne/zulip,brainwane/zulip,aakash-cr7/zulip,showell/zulip,hackerkid/zulip,krtkmj/zulip,vabs22/zulip,amyliu345/zulip,andersk/zulip,rht/zulip,Galexrt/zulip,joyhchen/zulip,christi3k/zulip,vaidap/zulip,ahmadassaf/zulip,esander91/zulip,j831/zulip,dattatreya303/zulip,brockwhittaker/zulip,ashwinirudrappa/zulip,ryanbackman/zulip,jrowan/zulip,JPJPJPOPOP/zulip,zacps/zulip,souravbadami/zulip,synicalsyntax/zulip,Frouk/zulip,brainwane/zulip,niftynei/zulip,samatdav/zulip,hackerkid/zulip,vakila/zulip,JPJPJPOPOP/zulip,dattatreya303/zulip,zacps/zulip,amanharitsh123/zulip,blaze225/zulip,isht3/zulip,AZtheAsian/zulip,showell/zulip,shubhamdhama/zulip,jackrzhang/zulip,showell/zulip,gkotian/zulip,ryansnowboarder/zulip,hackerkid/zulip,atomic-labs/zulip,jphilipsen05/zulip,isht3/zulip,jphilipsen05/zulip,atomic-labs/zulip,dawran6/zulip,rht/zulip,amyliu345/zulip,rht/zulip,andersk/zulip,dhcrzf/zulip,alliejones/zulip,rishig/zulip,esander91/zulip,christi3k/zulip,eeshangarg/zulip,Juanvulcano/zulip,esander91/zulip,gkotian/zulip,dwrpayne/zulip,amanharitsh123/zulip,j831/zulip,Jianchun1/zulip,Vallher/zulip,tommyip/zulip,peiwei/zulip,amanharitsh123/zulip,peguin40/zulip,peiwei/zulip,zacps/zulip,mahim97/zulip,blaze225/zulip,karamcnair/zulip,punchagan/zulip,andersk/zulip,cosmicAsymmetry/zulip,shubhamdhama/zulip,rht/zulip,showell/zulip,JPJPJPOPOP/zulip,kou/zulip,vikas-parashar/zulip,Frouk/zulip,Vallher/zulip,arpith/zulip,samatdav/zulip,jphilipsen05/zulip,TigorC/zulip,jphilipsen05/zulip,cosmicAsymmetry/zulip,Diptanshu8/zulip,Juanvulcano/zulip,jackrzhang/zulip,zulip/zulip,vabs22/zulip,vaidap/zulip,niftynei/zulip,vikas-parashar/zulip,arpith/zulip,krtkmj/zulip,synicalsyntax/zulip,amyliu345/zulip,arpith/zulip,isht3/zulip,niftynei/zulip,Diptanshu8/zulip,sup95/zulip,andersk/zulip,sup95/zulip,sonali0901/zulip,souravbadami/zulip,paxapy/zulip,hackerkid/zulip,jrowan/zulip,aakash-cr7/zulip,Jianchun1/zulip,ryansnowboarder/zulip,jainayush975/zulip,vaidap/zulip,zacps/zulip,timabbott/zulip,tommyip/zulip,TigorC/zulip,joyhchen/zulip,atomic-labs/zulip,jrowan/zulip,peguin40/zulip,alliejones/zulip,PhilSk/zulip,AZtheAsian/zulip,hackerkid/zulip,rishig/zulip,vikas-parashar/zulip,vaidap/zulip,jphilipsen05/zulip,sharmaeklavya2/zulip,dawran6/zulip,gkotian/zulip,kou/zulip,gkotian/zulip,synicalsyntax/zulip,rishig/zulip,Vallher/zulip,AZtheAsian/zulip,amyliu345/zulip,zulip/zulip,karamcnair/zulip,sonali0901/zulip,Galexrt/zulip,AZtheAsian/zulip,ryansnowboarder/zulip,tommyip/zulip,paxapy/zulip,synicalsyntax/zulip,jackrzhang/zulip,punchagan/zulip,shubhamdhama/zulip,sup95/zulip,brockwhittaker/zulip,Frouk/zulip,dhcrzf/zulip,dhcrzf/zulip,grave-w-grave/zulip,isht3/zulip,peiwei/zulip,alliejones/zulip,sonali0901/zulip,mahim97/zulip,punchagan/zulip,ahmadassaf/zulip,vabs22/zulip,atomic-labs/zulip,j831/zulip,atomic-labs/zulip,eeshangarg/zulip,vikas-parashar/zulip,arpith/zulip,ryansnowboarder/zulip,Galexrt/zulip,karamcnair/zulip,verma-varsha/zulip,Frouk/zulip,timabbott/zulip,blaze225/zulip,ashwinirudrappa/zulip,samatdav/zulip,brainwane/zulip,dawran6/zulip,paxapy/zulip,synicalsyntax/zulip,gkotian/zulip,KingxBanana/zulip,reyha/zulip,blaze225/zulip,dhcrzf/zulip,zulip/zulip,calvinleenyc/zulip,AZtheAsian/zulip,showell/zulip,aakash-cr7/zulip,krtkmj/zulip,jainayush975/zulip,amyliu345/zulip,shubhamdhama/zulip,grave-w-grave/zulip,krtkmj/zulip,SmartPeople/zulip,Galexrt/zulip,niftynei/zulip,andersk/zulip,KingxBanana/zulip,esander91/zulip,brockwhittaker/zulip,reyha/zulip,brainwane/zulip,peguin40/zulip,mohsenSy/zulip,tommyip/zulip,mahim97/zulip,Vallher/zulip,TigorC/zulip,mohsenSy/zulip,dhcrzf/zulip,brockwhittaker/zulip,arpith/zulip,dwrpayne/zulip,ryansnowboarder/zulip,verma-varsha/zulip,dawran6/zulip,sup95/zulip,Juanvulcano/zulip,atomic-labs/zulip,peguin40/zulip,sharmaeklavya2/zulip,punchagan/zulip,Frouk/zulip,calvinleenyc/zulip,joyhchen/zulip,ahmadassaf/zulip,esander91/zulip,shubhamdhama/zulip,mohsenSy/zulip,amanharitsh123/zulip,SmartPeople/zulip,j831/zulip,synicalsyntax/zulip,aakash-cr7/zulip,PhilSk/zulip,sonali0901/zulip,ryanbackman/zulip,andersk/zulip,rht/zulip,brainwane/zulip,souravbadami/zulip,sonali0901/zulip,zulip/zulip,jackrzhang/zulip,peiwei/zulip,samatdav/zulip,Vallher/zulip,calvinleenyc/zulip,krtkmj/zulip,brockwhittaker/zulip,peiwei/zulip,arpith/zulip,susansls/zulip,christi3k/zulip,dwrpayne/zulip,Jianchun1/zulip,sharmaeklavya2/zulip,susansls/zulip,PhilSk/zulip,reyha/zulip,Frouk/zulip,shubhamdhama/zulip,rishig/zulip,SmartPeople/zulip,Juanvulcano/zulip,Diptanshu8/zulip,esander91/zulip,Juanvulcano/zulip,KingxBanana/zulip,eeshangarg/zulip,TigorC/zulip,JPJPJPOPOP/zulip,timabbott/zulip,alliejones/zulip,brockwhittaker/zulip,vaidap/zulip,kou/zulip,PhilSk/zulip,vikas-parashar/zulip,gkotian/zulip,dawran6/zulip,punchagan/zulip,eeshangarg/zulip,dhcrzf/zulip,ryanbackman/zulip,umkay/zulip,vakila/zulip,JPJPJPOPOP/zulip,vaidap/zulip,Diptanshu8/zulip,mahim97/zulip,calvinleenyc/zulip,niftynei/zulip,timabbott/zulip,susansls/zulip