To reduce the amount of code and complexity of the service we move away
from a management command triggered by a cronjob, to a task handled by
django-q. Everything works the same way as before, but the management
command now schedules the task instead of doing it. Introduces the
ORGREG_SCHEDULE_TYPE settings variable controlling the scheduled when
scheduling the import using the management command.

The setup has five parts:
- a new email template type
- a new django-q task for notifying
- a management command for scheduling the task periodically
- a new settings variable NOTIFIER_LIMIT for controlling the number of
  days into the future the notifier script should use for end date of
  roles.
- a new settings variable NOTIFIER_SCHEDULE_TYPE for controlling how
  often the notifier task should be scheduled when using the management
  command.

Resolves: GREG-162

Done to make djangoq settings accessible in production.
The sync setting is changed to the default False value since the run
order of the tasks is not relevant for our use case.
Mail sending functions have gotten a sync argument to force the tasks to
complete before checking their consequences in tests.

- Set the default to IsAdminUser
- Set it explicitly on all the views
- Add tests

We do not use the token after initial login, no need to refresh.

Set cookie SameSite policy to Lax and skip the HttpOnly flag to allow the cookies to be used by the frontend

To prevent hammering on the invite endpoint we throttle requests to the
endpoint to 100/day per ip.

Resolves: GREG-84

To facilitate multiple identifiers of OUs we introduce the OuIdentifier
model and removed the orgreg_id field from OrganizationalUnit.

All current orgreg_ids are recreated as OuIdentifiers with name
'orgreg_id' and source 'orgreg'. Both values are configurable in the
base settings file in the gregsite app. Note that changing this value
after migration will require manual work changing all OuIdentifiers
already created before the next run of the orgreg_import management
command since that assumes all current orgreg identifiers uses these
values.

All endpoints that previously exposed the orgreg_id field now exposes an
identifiers field with a list of OuIdentifiers connected to that model
with fields id, name, source, and value.

Resolves: GREG-88

- Rename management command start_notification_publisher to notification_publisher
- Rename management command start_schedule_tasks to task_scheduler
- Stop using python-daemon and lockfiles, as these will run as standalone containers anyway
- Remove management commands stop_notification_publisher and stop_schedule_tasks
- Remove python-daemon dependency

Issue: GREG-66

Add a Containerfile for the frontend. Allow configuration to be injected. Move static files directory for Django.

Issue: GREG-36

Issue: GREG-36

Issue: GREG-36

Issue: GREG-35