Deal with feedbacks that are associated with deleted requests

Solution

• We should keep feedback
• This might require a custom @Query

Summary

Once the cascading deletes have been deployed, it will delete feedback along with requests. Obviously, deleted feedback might still be useful so we need to decide what to do with it. Issue #561 (closed) has some thoughts on this. I've also included a screenshot below.

EDIT: Copied from #680 (closed)

A student/ta should be able to see the feedback from a deleted lab (and hence also request). Given that it is anonymous, the student doesn't know to what request this is feedback should be attached so this should not be a problem if we stop fetching the request for feedbacks. The real problem occurs with admins who are able to see the request attached to the feedback, for them, we need to find an elegant solution.