Fix support for nullable UTCDateTime instances
Merge djmitche/build-relengapi:utcdatetime-fix (PR #105)
Move relengapi.celery to relengapi.lib.celery

..and clean up some docs.  Part of #86.
Merge djmitche/build-relengapi:relengapi.lib.celery (PR #108)
Merge commit '0edcff5' into slaveloan
Adjustment for celery lib change