Process jobs in two queues

[nickbradley]

Currently, only one queue manages all commit jobs. This has the drawback that commits students want to see the grade for may be behind many (unimportant -- to the students) other jobs.

Proposal. Create two queues: standard and express. All commits initially go into the standard queue. If a student requests their grade, the job should be moved from the standard queue and put into the express queue.

Assumptions.

• Commits always precede grade request (this might affect hook re-deliveries).

Edge cases.

• The requested commit job might already be being processed in the standard queue. (How to check for this?).