Changed the way that courses are handled in the database. Instead of
creating a new course object every time the user enters a course, users
now have a ManyToMany field that contains all of their courses. When a
user adds a course, if the course already exists, a relation to it is
added to their courses field. If it doesn't exist, a new course object
is added to the database and the relation is added to the user's courses
field.