Investigate using Girder as a Celery results backend

[cjh1]

If we need to move away from RabbitMQ it might be possible to implement a results backend that puts the results directly into Girder.

http://docs.celeryproject.org/en/latest/userguide/tasks.html#task-result-backends

[zachmullen]

I like this idea

[cjh1]

@kotfic Came up with it :-)

[kotfic]

ref: https://github.com/girder/girder_worker/pull/184