Django-modeltrans

- Allow adding `MultilingualManager()` as a manager to objects without translations to allow lookups
of translated content through those managers.

Initial release packaged from revision 19.

- Use proper alias in subqueries, fixes 23.
- Support lookups on and ordering by related translated fields (`.filter(category__name_nl='Vogels')`), fixes 13.
- Use `KeyTextTransform()` rather than `RawSQL()` to access keys in the `JSONField`. For Django 1.9 and 1.10 the Django 1.11 version is used.

- Check if `MODELTRANS_AVAILABLE_LANGUAGES` only contains strings.
- Make sure `settings.LANGUAGE_CODE` is never returned from `conf.get_available_languages()`

- Cleaned up the settings used by django-modeltrans [19](https://github.com/zostera/django-modeltrans/pull/19).
This might be a breaking change, depending on your configuration.

- `AVAILABLE_LANGUAGES` is now renamed to `MODELTRANS_AVAILABLE_LANGUAGES` and defaults to the language codes in the
django `LANGUAGES` setting.
- `DEFAULT_LANGUAGE` is removed, instead, django-modeltrans uses the django `LANGUAGE_CODE` setting.
- Added per-language configurable fallback using the `MODELTRANS_FALLBACK` setting.

- Also fall back to `DEFAULT_LANGUAGE` if the value for a key in the translations dict is falsy.