Update module to configure good job for background workers

[robbevp]

This PR matches accentor/api#478 and allows the user to configure both good job and delayed job. A next PR can remove the delayed job config.

I opted to have the user pass the names of queues instead of simply the amount of workers to allow more finegrained control.
The default still uses 4 workers (though now with 5 threads each). One of the workers is reserved for the most urgent items. The others will work off all queues in the order they are specified in the string.

[robbevp]

All the checks failing is unrelated to this PR

[robbevp]

Coming back to this: Our default workers for Good job might be a bit too much for most setups. I went for 4 processes (since this was the default with delayed job), but since these processes are now multi-threaded (and have 5 threads by default), that means that we can process up to 20 jobs at once.
I don't have a good view on the amount of jobs and concurrency of them in production, so can't say for sure.

[chvp]

I would consider that too much even for our setup. In the worst case we're transcoding 20 files at the same time, which is a load I wouldn't want the server to have. I'd start with what we have now, but only one process for all queues instead of three. If it turns out that this results in issues, we can always adjust later.

[robbevp]

Updated default queues to be 1 process (with the queues in order of priority)