* Minimum possible changes were made to merge CapaModule & CapaDescriptor into
one ProblemBlock class.
* There are no known changes in behavior.
* CapaModule and CapaDescriptor inherited from a number of classes which inherit
from XModule or XModuleDescriptor but did not depend on them. For all these
classes the methods were moved to mixins which did not inherit from either and
then these mixins were added to ProblemBlock in the order which maintains MRO.
Add a new waffle switch that allows us to assume zero grades for
learners who have no entry previously recorded, and another to
disable persisting grades for unengaged learners.
TNL-6691
Remove deprecated SingleSectionGrader. TNL-5987
Remove display_name and module_id from Scores objects
Update CourseGradeFactory.__init__ to not be user-specific
Update some callers to use CourseGrade class instead of "summary" dict
Remove no longer needed course_grades.py module.
Renamed django signal from GRADES_UPDATED to COURSE_GRADE_CHANGED
Small changes to the grades djangoapp
-sets up mock_get_score context handler
-fixes an issue with not invalidating lazy scores property
-code quality fixes
-query count optimization in PersistentSubscetionGrade.create
-adds atomic blocks to avoid IntegrityErrors corrupting an entire request
