Ability to dis-enroll from classes

As our characters grow up their interests in classes may shift. Being able to dis-enroll is particularly useful for grading. For example homework from year 3 and onwards (especially post-grad) usually wait a long while in the pile before they eventually get graded by ATs / teachers, so if older users still grade and could dis-enroll from first year classes for example the chance is higher for this homework to get back quicker.