Distinguish access to OH queue based on users

[sophiefeng18]

Instructors and students have different access to the OH queue:

• instructors can open and close the queue;
• instructors can remove students from the queue;
• students can only add themselves to an open queue.

Estimated effort for each task: high
Dependencies among tasks: #16 #21 #20
Milestones to indicate which sprint the issue should be completed in (Sprint 1, Sprint 2, Stretch): Sprint 2
Acceptance criteria that describes how you know this task is done: Test on sample instructor and student accounts to ensure they have the correct access to features