------------------
**Breaking changes:**
- `FieldTracker` now marks fields as not changed after `refresh_from_db`
respecting `fields` argument (GH-404)
- `FieldTracker` now respects `update_fields` changed in overridden `save()`
method (GH-404)
- `FieldTracker` now resets states after `pre_save()` and not anymore `save()`
signals, possibly altering the behaviour of overridden `save()`
methods (GH-404)
**Other changes:**
- Update InheritanceQuerySetMixin to avoid querying too much tables
- TimeStampedModel now automatically adds 'modified' field as an update_fields
parameter even if it is forgotten while using save()
- Replace ugettext_lazy with gettext_lazy to satisfy Django deprecation warning
- Add available_objects manager to SoftDeletableModel and add deprecation
warning to objects manager.
- StatusModel now automatically adds 'status_changed' field during save as an
update_fieldsparameter when 'status' is present in it to make sure it is not
forgotten.
- Update test requirements
- Move tests to GitHub Actions: https://github.com/jazzband/django-model-utils/actions
- Drop support for `Django 2.1`
- Add support for `Python 3.9`
- Add support for `Django 3.1`