Model changes (will affect API and DB)

Course Template and course number will no longer be needed linked to a Course; their only value will be to suggest drop-downs when creating a new course; but new courses are not limited by these suggestions. They can be updated automatically when courses are created.

Offerings should be promoted to contain all information (i.e. don't refer to a Course Template). "Offerings" is not standard venacular.

Rename existing Course to CourseTemplate
Rename Offering to Course

A playlist mixes two concepts: An upstream source and a list of videos to play to the user. Let's separate these out, so that a playlist for students can contain multiple videos from multiple sources.
Rename existing Playlist to VideoSource
Create a new playlist object that includes a list of video sources.

New Playlist object is a collection of VideoSources, and can include one off videos manually uploaded.