Admin can create a new course.
Only admins can create new courses.
Require authentication before viewing courses.
Only show courses a user is enrolled in.
Limit users to viewing enrolled courses.
Display message when no enrolled courses.
Remove role from enrollments.

* Easier to assign roles directly to the user (e.g. a user is a
  student or instructor for every course). This can be changed if
  we need more control in the future.
Merge pull request #15 from atsheehan/add_courses

Add courses