Archiver fixes

[ross]

We need to check the archiver to make sure it works as we would expect after the changes in #2732:

• Receive notification of a file that needs processing
• Check the file's DB entry and upload the file to the configured remote service
• Update the URL of the file (both in the file's DB entry and the resource)
• Once we're sure the file is safely archived, we should mark the file as being archived

so that we know it can safely be deleted at some point.

Maybe this could/should be implemented as a service rather than a celery task?

[ross]

Going to be reworked without celery.