Update development dependencies.
Add pillow to requirements.
Refactor test factories to new factoryboy version (more compatible with django 1.7)
Patch client test fixture with useful login method.

This removes django-testclient-extensions because
it doesn't compatible with django 1.7.
Remove django-testclient-extensions from requirements.
Add f (factories) fixture for avoid direct import of factories.

Factories imports models at compile time and with django 1.7 this
is not possible. For avoid direct imports at compile time, "f" test
fixture is added that imports factories at runtime (lazy).
Remove direct import of factories.

Replace it with lazy loading test fixtures.
Fix migrations related to wrong resolution of history entry model.
Fix HistoryResourceMixin class import.