Add subtitle data to video API
Change URLs to handle course keys properly.
Remove stripping of subtitle url querystring param.
Another template change to keep the course listing from timing out with  hundreds of courses.
Update to make the mobile REST API support multi-language transcripts.

This is still a work in progress as the course_id code is a total
hack. I got clarification on how opaque keys should be used for this
but haven't had time to fit it in yet.
Remove runtime system init from mobile video API.

We only ever needed it to run the XBlock/XModule handler for
transcripts, and we no longer invoke that directly.