Django 1.7 and python 3.4 compatibility

fix(admin) - Renamed queryset method to get_queryset given the previous naming convention is deprecated.

fix(models) - Replaced get_user_model with settings.AUTH_USER_MODEL as recommended in django 1.7.

fix(migrations) - Moved south migrations to south_migrations directory.

fix(tests) - Added sites field to AdBase objects on create to be retrieved by the ad manager.

fix - More django 1.7 - python 3.4 compatibility fixes.