[ENHANCEMENT] Priority across queues

[xia-steven]

It would be nice if the priority of students persist across multiple queues in the same course. This prevents students from queuing for one queue then join another queue for (say another location) with their priority untouched

[nelsontm]

+1

[lslavice]

Also, it would be fantastic if we could somehow limit students to joining one queue per course, for basically the same reason -- to prevent them from trying to game the system when we're trying to help by having OH at multiple locations 🙁