Changes to vux (adult education) enrolments

SS12000 changes

* Fewer enrolment objects. Before this release, vux students would often have multiple enrolment objects for the same school and education level that occupied the same dates. There could for example be one enrolment object for 2020-08-06 to 2021-05-02 and another for 2020-08-04 to 2020-11-06. After this release, vux students will get the minimum number of enrolment objects required to describe the dates, schools, and education levels for the studies. The student from the previous example would get a single enrolment object for 2020-08-04 to 2021-05-02.