LEARNER-1894
This commit adds in course messaging for three use cases. First,
when the user is not signed in, the user is shown a message that
provides a link to sign in or register. If the user is signed in
but not enrolled, they are given a link to do so. If the user is
enrolled but the course has not yet started, they are shown a
message explaining when the course starts and shown a link (not
yet enabled) to add a reminder to their calendar.
The implementation defines a base message class and extends it
for the course home messages as well as the previously implemented
page level messages.
Extends the Programs ConfigurationModel, cleans up Programs-related utilities and corresponding tests, and corrects caching. Uses the Programs API to list programs within Studio. ECOM-2769.
