Do not auto-fill the course code in stuedent registration form

[Ivan Oleynikov]

Students often pick a wrong source code when registering. This might be due to “course code” field being pre-filled for them, so they are just clicking “Submit¨ without paying attention to the field and registering with the course code that is in the field by default.

It might be a good idea to make the “course code” field empty by default, and force student to explicitly pick something. Hopefully, this will decrease the number of incorrectly chosen course codes.

This change was originally proposed by John Hughes, who has this issue in his course.

Ivan