[DEV-1371] Add USE_TZ setting to settings.py and settings.py.mustache.
[DEV-1371] Amend add_tz_offset filter to use timezone-aware objects.
[DEV-1371] Replace all (uncommented) instances of datetime.datetime.now with timezone.now. Modify imports to accomodate this change.
[DEV-1371] Add timezone-aware migrations module. Replace calls to datetime.datetime.now with calls to timezone.now.
[DEV-1371] Replace specific calls to datetime with calls to timezone.
[DEV-1371] Replace imports of datetime with import of django.utils.timezone in new migrations module.
[DEV-1371_new_migrations] Add tzinfo argument to datetime calls that is set to UTC if 'USE_TZ' is True in settings or None otherwise.
[DEV-1371_new_migrations] Overwrite existing migrations with new timezone-aware migrations.
[DEV-1371_new_migrations] Add missing timezone import.
[DEV-1371] Continue replacing imports and usage of datetime.now with timezone.now.
[DEV-1371] Update django_authopenid migrations to use timezone.now instead of datetime.now.
[DEV-1371] Update group_messaging migrations to use timezone.now instead of datetime.now.