refactor(controller): optimize layer creation

This restructures the Dockerfile in such a way that allows users to rebuild the
controller with minimal changes to the docker image's layers.
fix(controller): update Dockerfile maintainer
Merge pull request #1246 from deis/dockerfile-optimization

refactor(controller): optimize layer creation
chore(controller): update Django to 1.6.5 security release

https://www.djangoproject.com/weblog/2014/may/14/security-releases-issued/
chore(controller): update South to 1.0 final release

http://south.readthedocs.org/en/latest/releasenotes/1.0.html