[WIP] Upgrade to Django 1.7

Upgrading to Django 1.7 requires the following:

- [ ] [Upgrading Django to a newer version](https://docs.djangoproject.com/en/1.7/howto/upgrade-version/).
- [ ] [Upgrading from South](https://docs.djangoproject.com/en/1.7/topics/migrations/#upgrading-from-south).
- [ ] [Upgrading to django-registration-redux](http://stackoverflow.com/a/25836530/2422398), since django-registration is no longer maintained and doesn't work with 1.7.
- [ ] Upgrading to dj-static 0.0.6, which added Django 1.7 support in https://github.com/kennethreitz/dj-static/commit/0b3e3a4b565d501e104ee55734bf9d60f81e3ec6.