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