Permissions cleanup/fixes

* Added a missing migration file
* Removed too-specific permission classes
* Fix to make sure scopes are still in the API spec

Improved testing tools

Authorization feature release

* Checking actions before object level permissions
* Implemented syncing permissions after fetching from AC
* Added convenience property to retrieve authorizations for request
* Added testing utils for new authz format

Fix crash when relativedeltafield is not installed

Fix refactor mistake

Refactored some auth bits and pieces

* Configuration model is merged in the authorizations app
* @action_description decorator removed
* Defaults for ClientConfig are now properly overridden

Fixed a bug in serialization of GroepAttributen

Only primitive types worked correctly, which is now fixed.

🔖 Bumped to version 0.40.0

NOTE: Bumpversion config already said 0.40.0 as current version but no
tag or release was made to PyPI, and setup.cfg also said 0.39.0.

Fix packaging

Started authorization models