Parent comm panel fix

Fixes commpanel bug with e-mailing parents

Because there is no Program.parents() method, the commpanel filters for Guardians and Educators was failing. Refactored the UserSearchController to always use the user type name (Student, Teacher, etc.) rather than the filter method names (students, teachers, etc.), and separated Guardians and Educators into their own categories (rather than grouping them under parents) to avoid this problem.

I want to merge this into stable because it is a problem that Yale Splash is experiencing right now, and I want to fix it for them ASAP, before we deploy the new stable release. After this is code reviewed and merge, we can also merge it to main.

I want someone to both code review and test this, because I made some interesting design choices / changes. I did do a bunch of testing on my own dev server, and everything seemed to work after I made my changes.