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/

It is not a good idea to output times this way as this is not appropriately localized. I would look at how dates are rendered elsewhere, e.g. on the course outline page. I forget the details but it may be that you have to render the date on the server so that Django format localization can be used:

https://docs.djangoproject.com/en/dev/topics/i18n/formatting/