Improvements to Delete Endpoint and Statuses

[haroldrubio]

Resolves

• Expertise API: Change Delete Endpoint #166
• Statuses are not properly set #156

This PR contains the following changes:

• Switches the /delete endpoint to POST
• Adds a new status Revoked to the JobConfig
• Fixes a bug where jobs that were waiting to have their scores computed were displayed as running, now they are shown as queued for expertise
• Adds the JobConfig as a dict to the Celery task arguments so the job information is visible when querying the queue by the Celery CLI
• Changes the logic of the /delete endpoint:
  • If called on a running job (any job whose status is not error or completed), sets the status to revoked, the job maintains the revoked status and gets cleaned up after making a final check in the expertise Celery task
  • If called on a non-running jobs (either error or completed), cleans the files on disk and removes the job from Redis
• Changes the high load test (which queues 5 jobs) to revoke the last job and checks that it was cleaned up correctly

[melisabok]

the changes look good!

I'm wondering if this PR is still active: #137

I think the jobs that were running and the server is restarted should be change to status "revoked", right?