- for self paced courses, if a sequential's due date has passed
and it is incomplete, allow the user to reset the start_date
for the related schedule to now, thus shifting all due dates
for all sequentials within the course by the pre determined
due date offset.
- add historical table to the Schedule model.
* Fix type mismatches in the course_modes migrations
* Fix type mismatches in the course_action_state migrations
* Fix type mismatches in the schedules migrations
* Fix type mismatches in grades migrations
* Fix type mismatches in video_pipeline
* Fix type mismatches in api_admin
* Fix mismatches in credential migrations
Django 2.0 will make this field required for `ForeignKey` and `OneToOneFields`.
In previous versions the option defaulted to `models.CASCADE` when not
specified. This change should make the deprecation warnings in the current
Django version go away.
The migrations where also modified, but the changes should not cause a change in
the database schema since `models.CASCADE` was already the old default.
