Mobile/studio video upload

https://openedx.atlassian.net/browse/MA-104
@andy-armstrong please review.  This is the initial PR for the video upload pipeline work.
@gwprice please review.
@doctoryes FYI - first usage of the AssetMetaData store.

I think this should be ```complementary```, unless we're complimenting people on their videos. :-)

http://the-word-blog.com/2010/04/12/complementary-vs-complimentary/