Django 1.7 support

All tests passing when not using migrations.
Problems in generating  working migrations, possibly due an error in Django migrations

* [x] Make tests run on 1.7
* [x] Fix code compatibilty
* [x] Make tests pass on 1.7
* [x] Make tests pass on 1.6 and previous

No django 1.7 migrations in this PR
* Create Django 1.7 migrations

Fixes #3277