This commit is a rough port to Django 2.1, Python 3 and a Docker based local
development setup. Tests fail/error but migrations and the web frontend are
already runnable. Task queue functionality is untested and translations seem to
have trouble.
This commit isolates the celery task invocations of the userdbs app into
signal handlers. All celery interaction is now asynchronously handled in
userdbs.signals.
- modify userdbs.models.UserDatabase.delete to perform deletion of database
user if it has no other databases assigned
- implement userdbs.views.DeleteUserDatabase
- add URL pattern 'delete_userdatabase' to userdbs.urls
- add template userdbs/userdatabase_confirm_delete.html
- add link to 'delete_userdatabase' on hosting package detail page
- add changelog entry