chore(controller): update to Django 1.7

https://www.djangoproject.com/weblog/2014/sep/02/release-17-final/

The main effect for us is that South was removed in favor of Django's built-in `migrations` app. This means users with older versions of the controller's database schema may not be able to upgrade their DB in-place, although anyone using v0.11.0 or later should be fine--this needs to be tested specifically. 

There may be a gentle way to move forward from our very earliest schema to the current one, but it involves running south migrations using Django 1.6 against the old schema, then removing all mention of south and running Django migrations using 1.7--not something we could easily automate in the boot script.