API and UI to delete and/or archive jobs

[sampsyo]

As @ViviYe has proposed, it would be nice to have a way to delete jobs. Some concrete steps could include:

• Add a DELETE method on job URLs that removes the job and all its files.
• Add a button to the UI that invokes this API method.
• Perhaps a second API that just deletes the files but preserves the metadata (i.e., the JSON file describing the job and its log file).
• In a fancier version, provide a mechanism to delete a job's files while sending it to S3 or something for archiving.
• Maybe provide a way to do this in bulk to jobs older than a certain date?

(Expanded from #1.)

[rachitnigam]

As a first pass, implementing something that removes jobs from instance/jobs and compresses them for download would be useful. We can move the compressed jobs to the gorgonzola deployment and the various job links still work.