Fix to playlist JSON to update bad unit.
Ordering tweak: show grade level before unit in playlist titles.
Calculate points correctly and give points during fixed block.

Also, mark the exercise stage (normal vs _fixedblock vs _completed).

Plus, other random exercise-related fixes and tweaks.
Merge branch 'nalanda-rct3' of github.com:learningequality/ka-lite into fix_exercise_points
Merge pull request #2567 from jamalex/fix_exercise_points

Calculate points correctly and give points during fixed block.