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.
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