Pseudo-randomize exam order in queue

My concern is always that I might be more lenient when I start grading and gradually become stricter (or possibly the other way around). This effect would somewhat cancel out if different problems are graded in different orders.

Sorting the exams completely randomly every time might not be a good idea (having the same order when re-creating the queue is probably useful). Maybe something like sorting by hash(problemid, instance) could work.

I'm not fully convinced that this is a good idea, but I am somewhat concerned about this potential systematic bias.