Implementation for DE-1089.
Centralize the definition of context into a single method. This is in
common/djangoapps/track because the context is originally set there by
middleware.
Ensure an event is fired whenever a student updates/creates
its course goal.'edx.course_goal.created' and 'edx.course_goal.updated'
should be sent after creation and updation respectively.
LEARNER-3352
LEARNER-2308
Once a goal has been set for a user on the course home message,
allow them to update it on the course home side bar. Automatically
sets a course goal for users when enrolling in a verifiable course.