Fix Djangop 1.4 compatibility

Ignore `update_fields` value in the save_base() function,
as this was included with Django 1.5. Removed from signals
as this wasn't used yet anyways.
Fix model loading for tests, avoid model scan in model construction

The get_field_by_name() function also checks for related fields, and
starts a model scan. Using get_fields_with_model() instead which only
checks local fields of the model itself.
Save all models which were fetched in the cache.
Fix passing _current_language to the model __init__ function
Added unit tests for models and forms
Remove no-op code, doesn't happen in __init__
Fix sending pre_translation_save signal
Update changes
Added travis and tox.ini