Video play problem on next button fixed

This was a fairly tricky one, see: http://stackoverflow.com/questions/20749622/jquery-ujs-has-already-been-loaded-rails and http://stackoverflow.com/questions/22838515/loading-javascript-with-turbolink-plugin which have similar problems (though their specific fixes didn't work since they didn't include the youtube api).

The comment in the code explains what is going on. In short, the turbolink plugin causes API ready events to not always be triggered, so we track that with a global variable ourselves and call it when needed.
On Wed, Jun 11, 2014 at 09:34:14AM -0700, Brian Sadler wrote:
> Love the comments here!  Very clear and useful.

yea, that was a painful bug to track down (I didn't even know the
turbolinks thing existed; it was kinda a guess to find it too) so
I wanted to write that up so we remember for later.