Change groups & submissions from the dashboard

[Sumukh]

Staff can view:

• A students group
• Their submission/backup history from the staff dashboard

Staff can perform any of these actions (even after the deadline):

• Change groups
• Change flags
• Upload new submissions
• Change grades

This PR resolves the following issues

• Resolves Sudo Mode Improvements  #787
• Resolves Ability to inspect/edit groups from admin view #771
• Resolves Staff should be able to replace a students Final Submission #613

[Sumukh]

I'm going to merge this for the start of the semester, but it'd be nice if this was still reviewed. I'll add integration tests for this later so we get back up to > 70% coverage.

I tested the changes on staging and things worked. I really wish we had this a few semesters ago. 😬