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.

Thanks for the gentle feedback.  ;)
Hmm.. this is exactly a conversation I had with @doctoryes a while back.  Studio is currently inconsistent with the way it handles this.  I've essentially kept this code conformant with the tabs handler in Studio.