Activity Feed minibar update alerts

Minibar update alerts are now generated when Activity Feed posts and comments are added to a unit you are enrolled in. This allows learners to stay up to date with new posts from instructors, and instructors to keep up to date with any new comments added to their posts by learners.
Note: Everyone enrolled in the unit, except the post author, receives a minibar update alert when a new post is created. Only the post author receives minibar alerts for new comments.