Unassign all group on unit switching, #2535
Allows student to view playlist that belong to previous units
Teacher are not allowed to assign future playlist #2490
Merge pull request #2538 from anuragkanungo/future_playlist

Teacher are not allowed to assign future playlist #2490
Code Refactoring - Added Method playlist_group_mapping_reset_for_a_facility
Added Tests
Tweak to allow student report page to be viewed on central server.
Merge branch 'nalanda-rct3' of github.com:learningequality/ka-lite into nalanda-rct3
Merge pull request #2536 from anuragkanungo/anurag

Unassign all group on unit switching, #2535