[Tagging] Copying tags when using library content in a course

[bradenmacdonald]

"As a content author, when I import library content into a Course, I expect the tags to be copied over as well"

"As a content author, when I import library content into a course, I can add my own tags to that content."

Acceptance Criteria

Based on the discovery findings from #177, implement the following:

1. Tags that are added to a piece of content in a library stay with the content when it's imported to a course.
2. Tags that were added from a library cannot be deleted from the course.
3. Users can add new tags to library content when it is being used in a course, but those new tags don't sync back to the Library version of the content.
4. When the piece of content is refreshed to use the latest version from the library, its tags will be refreshed as well (tags that were added to the library version get added to the course version; tags that were removed from the library version get removed from the course version; tags that were added to the content within the course are preserved unchanged).

This only applies to v2 Libraries ("Libraries Relaunch") based on Learning Core / Blockstore - not modulestore.