and CourseSectionSequence to ensure that cascading deletes will occur to delete
the relation upon deletion of a foreign-keyed object.
This commit is phase 1 of 3 in order to ensure a smooth deploy. The phases:
1) Add separate through models for user partition groups, add fields to point to the
separate models, and start writing to those fields as well.
2) After all models have been re-generated, switch code over to use separate through
model fields backed by the separate through models.
3) After phase 2 is deployed smoothly, remove the original ManyToManyField fields
and rename the new fields to have the same name as the old fields.
a9b534e10b