* Initial work on #13381
* Fix backend type display in table column
* Fix data source type choices during bulk edit
* Misc cleanup
* Move backend utils from core app to netbox
* Move backend type validation from serializer to model
* Move extras.plugins to netbox.plugins & add deprecation warnings
* Move plugin template tags from extras to utilities
* Move plugins tests from extras to netbox
* Add TODO reminders for v4.0