Add resque gem (#44).
Add Rails4 ActiveAdmin glue; missed this a while ago.
Connect Resque to Airbrake.
Start to trim away old DJ stuff (broken commits ahoy!).
Remove DJ initializer.
Add support for Paperclip files in the database (#44).

This means that remote job workers will be able to work off jobs
and then send the results to the database, rather than saving
them as physical files on disk.  Right now that's only implemented
in UploadedAsset; more to come.
Switch AnalysisTask#result to a Paperclip attachment.
More transitioning away from the Download class.
Migrate from delayed_job to Resque (closes #44).

This commit is, unfortunately, *way* too big.  I *guarantee* there
are bugs in here.  We've simultaneously had to switch from DJ to RQ,
move file attachments into the database using Paperclip and the
paperclip_database storage backend, deploy a new controller action
for showing uploaded asset images, update a bunch of our job parameter
passing logic, rework the specs, rework Airbrake error handling, and
so on, and so on.

The specs pass, but I'm going to start now to bash on some testing
of the job workers, to see if things actually work as they're
supposed to.