Enrollment uniqueness

[ShootingStar91]

Check if it's possible to change enrollments that are taken in updater into oodikone to unique per course_unit_realisation_id (only one of each state).

Because there may be loads of unnecessary duplicate-enrollments for same course realisations, that are likely not needed anywhere in oodikone, and they mess up the numbers if counting enrollments.

OR simply bring the realisation id into oodikone. This could be good fix although its weird to have ID's which will not refer to anything else in the db