Store Missing Prerequisites in Groups

[Awesome-E]

Right now, missing prerequisites are stored as just strings of the courses that need to be completed. This does not account for "OR" cases, where only one of them need to be completed, i.e ICS46 OR CSE46. It currently will say "ICS46, CSE46" in missing prerequisite texts, but there should be some indication that only one actually needs to be completed.

Original discussion/PR: #584 (comment)