Initial support for dubbed videos

This fully addresses #1103; please see that PR for changes.

The UI is not done, but is currently blocked from progress until an issue with KA can be solved (soon!).  Meanwhile, support can be tested.

* Now, the pre-video topic page should:
    * Show availability, based on any language having a video available.
    * Show you all available videos (in red), and all available subtitles (in blue).
* When you visit the video page,
    * It'll show you the english language videos (hard-coded until the above can be solved)
    * You should have all subtitles available.

How to test:
* Download an english video
* Find a language for which there's a dubbed video youtube ID, and copy the video file and rename the copy to that youtube ID.
* Go to the pre-video topic page, and you should see both languages showing in red.  Note there's a bug such that subtitles will show twice; I'll address that in a UI-only PR, once the above is solved.

![image](https://f.cloud.github.com/assets/4072455/1607067/1090febe-546d-11e3-8f2a-40af90ab833f.png)