Fix fencepost error in Tutor#schedule_for.

When iterating the blocks, we don't want to produce a block *starting*
at the end time.
Include Enumerable in TutorDaySchedule.

Clean up the interface a bit.
Use Tutor#schedule_for in template.

Need to test this still.
Test for appointments appearing in schedule table.

Confirm that Tutor#schedule_for integrates with the view code properly.