Added mezzanine-mailchimp to third party apps in README.
Added mezzanine-mailchimp to third party apps in README.

dekomote/mezzanine-modeltranslation-backport,wbtuomela/mezzanine,sjdines/mezzanine,Cajoline/mezzanine,dsanders11/mezzanine,Kniyl/mezzanine,agepoly/mezzanine,sjuxax/mezzanine,biomassives/mezzanine,theclanks/mezzanine,damnfine/mezzanine,Cajoline/mezzanine,Skytorn86/mezzanine,spookylukey/mezzanine,AlexHill/mezzanine,industrydive/mezzanine,gradel/mezzanine,nikolas/mezzanine,sjuxax/mezzanine,viaregio/mezzanine,theclanks/mezzanine,emile2016/mezzanine,sjuxax/mezzanine,adrian-the-git/mezzanine,ryneeverett/mezzanine,jjz/mezzanine,spookylukey/mezzanine,emile2016/mezzanine,mush42/mezzanine,Cajoline/mezzanine,PegasusWang/mezzanine,joshcartme/mezzanine,ZeroXn/mezzanine,frankchin/mezzanine,eino-makitalo/mezzanine,saintbird/mezzanine,mush42/mezzanine,promil23/mezzanine,agepoly/mezzanine,promil23/mezzanine,tuxinhang1989/mezzanine,industrydive/mezzanine,wbtuomela/mezzanine,ZeroXn/mezzanine,dekomote/mezzanine-modeltranslation-backport,adrian-the-git/mezzanine,dsanders11/mezzanine,agepoly/mezzanine,webounty/mezzanine,vladir/mezzanine,webounty/mezzanine,adrian-the-git/mezzanine,christianwgd/mezzanine,geodesign/mezzanine,jerivas/mezzanine,geodesign/mezzanine,webounty/mezzanine,readevalprint/mezzanine,nikolas/mezzanine,dovydas/mezzanine,molokov/mezzanine,wyzex/mezzanine,molokov/mezzanine,batpad/mezzanine,jjz/mezzanine,dovydas/mezzanine,SoLoHiC/mezzanine,batpad/mezzanine,douglaskastle/mezzanine,joshcartme/mezzanine,PegasusWang/mezzanine,christianwgd/mezzanine,biomassives/mezzanine,spookylukey/mezzanine,Kniyl/mezzanine,jerivas/mezzanine,vladir/mezzanine,damnfine/mezzanine,eino-makitalo/mezzanine,stephenmcd/mezzanine,gradel/mezzanine,cccs-web/mezzanine,SoLoHiC/mezzanine,frankier/mezzanine,sjdines/mezzanine,PegasusWang/mezzanine,biomassives/mezzanine,promil23/mezzanine,saintbird/mezzanine,frankier/mezzanine,Cicero-Zhao/mezzanine,AlexHill/mezzanine,damnfine/mezzanine,molokov/mezzanine,Kniyl/mezzanine,vladir/mezzanine,douglaskastle/mezzanine,stephenmcd/mezzanine,jjz/mezzanine,dustinrb/mezzanine,gradel/mezzanine,christianwgd/mezzanine,wbtuomela/mezzanine,douglaskastle/mezzanine,Skytorn86/mezzanine,dustinrb/mezzanine,mush42/mezzanine,ryneeverett/mezzanine,cccs-web/mezzanine,frankchin/mezzanine,ryneeverett/mezzanine,saintbird/mezzanine,jerivas/mezzanine,dekomote/mezzanine-modeltranslation-backport,viaregio/mezzanine,readevalprint/mezzanine,readevalprint/mezzanine,tuxinhang1989/mezzanine,nikolas/mezzanine,frankchin/mezzanine,dsanders11/mezzanine,emile2016/mezzanine,industrydive/mezzanine,wyzex/mezzanine,Skytorn86/mezzanine,tuxinhang1989/mezzanine,sjdines/mezzanine,frankier/mezzanine,Cicero-Zhao/mezzanine,eino-makitalo/mezzanine,wyzex/mezzanine,dustinrb/mezzanine,fusionbox/mezzanine,viaregio/mezzanine,joshcartme/mezzanine,geodesign/mezzanine,dovydas/mezzanine,theclanks/mezzanine,stephenmcd/mezzanine,fusionbox/mezzanine,ZeroXn/mezzanine,SoLoHiC/mezzanine