* fix: add error handling for potential issues calculating course progress
Realized there is potential in a few places for exceptions to be thrown. I'm adding some more error handling in the course progress task and function to handle potential issues.
This PR attempts to improve the ability to collect analytics about learner's progress
in their courses. Currently, the only place we regularly calculate course progress is
when a learner visits the "Progress" tab in the courseware.
Now, _optionally_, when a learner visits the home page of their course, we will enqueue
a Celery task that will calculate their progress and emit a tracking event.
This event is gated by use of the COURSE_HOME_SEND_COURSE_PROGRESS_ANALYTICS_FOR_STUDENT
waffle flag.
Previously, the course grade returned would be the stored grade,
which is calculated for all content, not just the visible grades.
(Some grades are not yet released to the learner.)
This fix recalculates the overall grade before sending to the MFE,
so that it doesn't have to recompute it itself (without all the
particular logic that the platform uses when grading).
AA-1217
* Add unsubscribe_token uuid field to CourseGoal model
* Add endpoint to unsubcribe from just a token (no login needed)
* Add admin page for the course_goals djangoapp
* Add get_course_overview_or_404 utility method
* Clean up URL handling in course_home_api
AA-907
