Consider migrating BG Tasks to Celery

[ghukill]

Not sure how, or if, this is possible with Django Background Tasks. Perhaps restarting the supervisor listening process is a possibility? or would that trigger retries?

[ghukill]

This has proved to be pretty important functionality.

Unfortunately, it might suggest looking at a more robust bg task framework like Celery.

[ghukill]

Scaffolding begins in celery branch, looking hopeful it will nicely address scaling, extensibility, and blocking nature of django bg tasks.

[ghukill]

Consider callback for closing task, updating timestamp, etc.?

[ghukill]

Done. Fairly major change, but much of the work was swapping out Django background tasks for celery, while scaffolding for CombineBackgroundTask was already in place. Likely issues and bugs will arise, but will open seperately. Closing here.