Alex/multiple transcripts editor

Create an upload modal for video transcript translations (BLD-751: https://edx-wiki.atlassian.net/browse/BLD-751).
![screen shot 2014-03-24 at 10 00 05](https://f.cloud.github.com/assets/1247491/2498141/68e9083e-b342-11e3-8904-300e4d9dccb2.png)

@cahrens please review
@valera-rozuvan please review
@frrrances please review
@dmitchell please review.
@olmar please review python part