Rewriting the check availability page

New version of the check availability page:
All timeslots are shown, in order, whether or not the teacher is available
Four colors: gray for unavailable, blue for available, black for teaching, orange for teaching but not available (colors chosen for accessibility reasons, this was the best thing I could come up with after green/red)
Shows names and rooms of classes under the timeslots and links to the manage page for the class
Shows list of teacher's unscheduled classes at the bottom, with duration