Make course durations more readable

For course durations, if it's over 60 minutes, things just get messy.
Especially if courses go several hours total.  So we'll make them nice
and readable, e.g.:

  30 minutes  => 30m
  60 minutes  => 1h
  90 minutes  => 1h 30m
Merge branch 'master' into human-readable-durations

Conflicts:
	test/models/course_test.rb
Merge pull request #12 from cit-jmu/human-readable-durations

Make course durations more readable