Add CSV download button to Studio video upload page

@nasthagiri @clrux @BenjiLee 

http://studio.gwprice.m.sandbox.edx.org/videos/vpip/vpip/vpip
Question: Do you know what the Studio convention is for underscore-file variable names?  I notice it is not consistent in the codebase.  Some have `camelCased` variables and some have `underscore` ones.