Teachers are not enrolled to a course

[EliasC]

Because teachers are not enrolled to a course, trying to log in as a student (for demonstration purposes) causes an error. There are two solutions to this that I can think of:

1. Change the check for current enrolment so that teachers automatically get a dummy enrolment.
2. Remove the concept of enrolment entirely. We are currently spinning up a new instance of Bubify whenever we have a new course or course instance, so removing enrolment from the code would reduce complexity.