Change video transcripts to use locators instead of locations.

STUD-870

@auraz and @polesye Please review this PR (including checking it out and testing the video transcript workflow manually). All tests are passing, but I don't know how these functions work well enough to manually test myself.

I did consider leaving some of the variable names as "component_id" instead of changing to "component_locator" (to reduce the number of changes in the PR). However, that was causing me confusion when trying to understand if I changed everything that I needed to. 

I have not done anything to the form of the URLs. Since changing video transcript URLs to be RESTful is not necessary for unblocking the database re-architecture epic, we have decided to postpone that work.