Updated confirmation messages to use Rails Flash message
Cleaned up error notification for students

Now when students try to click the 'Start a course' button, they will get redirected to the dashboard with a flash[:error] = "You don't have permission to access that page".

This makes it consistent how Canvas handles with access denied events.
More code cleanup
Added Nil checker when retrieving terms["teachingSemester"] from the REST server
Merge pull request #29 from ronvs/course_form

Course form