Track additional events

The goal is to eventually add tracking for the following actions:

* Click the "help" button at the top of the page
* Hover over the "more info" icons

This is an early review so that I can get early directional feedback before investing too heavily in a particular approach.
I like the `TrackedViewMixin` idea. If you go this route, be sure to refactor `CourseContextMixin` as well.