Support Django 1.7

* Django 1.7 needs to be explicitly setup in standalone scripts
* Silence Django warnings and setup required middleware (request.user,
  messages)
* Make Mock requests pretend to be HttpRequests
* Fix a couple of typos and broken links in documentation
* Don't allow 1.7 failures with Travis
* Remove INSTALLED_APPS overrides in tests since they don't work with
the app loading refactor
* Move old migrations and create new 1.7 migrations
I tried that first. The only issue was that the code fails because it tries to access `request._messages` to use the `django.contrib.messages` framework. I could mock that out too, but this seemed simpler.