WIP: video_modules now uses edxval to fetch mp4 video values

@ormsbee
Definitely the wrong thing to do, but not sure about the better thing in the short term. Here's the deal: the VideoModule should be using edx-val to figure out what URL to give for video resources. edx-val is a Django app, and including it causes Django dependencies to be introduced into common/lib. So the choices seem to be:

1. Move VideoModule out of edx-platform (expensive).
2. Accept the Django dependency in common/lib (explicitly discouraged).
3. Do this so that the code is still functional when called within the context of the LMS, but does not cause failure on import when running standalone tests.

Most VideoModule tests tend to be in the LMS anyway.

I want to do (1) here eventually. Any suggestions for a more elegant short term fix?