Add functionality to "block out" certain rooms for certain times during a given semester

Only an admin would be able to block out time blocks in these rooms.  If certain times are blocked out, a user would not be able to put a class in that room during that time.  This could be used to block certain times for lab rooms (such as set-up times) if those lab rooms are also used as classrooms sometimes, or to block out (say) the "courtroom" during certain morning hours.