Add video upload feature to Studio

This still needs to be audited for accessibility.

Please review: @nasthagiri @andy-armstrong @frrrances @talbs 
FYI: @clrux @doctoryes @karadhya 

*JIRA Tickets:*
* https://openedx.atlassian.net/browse/MA-28
* https://openedx.atlassian.net/browse/MA-85
* https://openedx.atlassian.net/browse/MA-86

*UX Design:* https://edx-wiki.atlassian.net/wiki/display/UX/Video+Uploads+in+Studio
*Functional Spec:* https://openedx.atlassian.net/wiki/display/MA/Video+Pipeline
*Sandbox:* http://studio.video-pipeline.m.sandbox.edx.org/

I agree. IMO we should not preemptively render alerts like this. We have shared Backbone views that can add alerts dynamically to a page when they are needed.

The way I think about the Mako templates is that they should render only what the user should see immediately. Such content is better coming from the server because it will render directly into the page with no delay, as opposed to a Backbone view which has to be evaluated in JavaScript to produce its content. The downside to server side content is that it has to be downloaded by the user every time and it cannot be cached. Cutting unnecessary content out of the page response is one useful way to improve performance.