Student blacklist

[jacksontromero]

Idea from the big man himself (Iliano), but he wants eventually a way for Admins to specify students who are blacklisted from the OHQ to deal with problematic students who misuse OH resources. So adding a list to admin settings, storing whether a student is blacklisted in the DB, and maybe having a configurable pop-up message that blacklisted students get would be good things to do resolve this.