text: Title: Remove stated support for Django<1.8
  Body: We don't have a clear support policy, but the Django team no longer supports Django<1.8; let's remove it as well.
  
  This means:
  - Removing it from the tox.ini matrix
  - Removing it from the README.rst and other docs, if needed
  - Finding any code that looks for ``django.version`` and remove code paths used for Django<1.8