Active subjects

Paged view that will display the JoinedSubject entities that are requested in at least one TeacherSubjectAllocation or that contain a mandatory subject in some of the study programs. The display view should be similar to the JoinedSubject crud page, only without the actions column.

The current filters should remain, but additional filters for the semester of the subject (`WINTER/SUMMER` or semester number) should be implemented.

This list will be shown on the public site so that the students will know which subjects will get activated for enrollment.