[Studio] Enable Studio Comments to be Universal

[lshulman]

By "universal" I mean to not limit instructor comments to one specific course.

If I create/use a Studio video I want to use in more than one course and I add comments for students to reply to (e.g. answer questions as they watch the video), I want to be able to use the video with my comments in multiple course sites, reuse it over multiple semesters. Current functionality only allows the comments to appear in the one course site they are created in. 

Better functionality: instructor adds comments in Studio, before embedding in a course site. And all of those comments will be included when the video is embedded in the course site (rather than having to create the comments after the video is embedded in the course site). Then the video with comments can be added to any number of course sites, reused over multiple semesters. The comments the instructor adds in Studio do not get lost when embedding it into a course site.

Naturally, student responses or additional comments added within a given course site, after the video is embedded, will only be maintained in the specific course the student is in.