Add tracking for YouTube videos #2156

This is a WIP. I'm tracking the following events right now

1. Load event for YouTube videos
2. Play/Paused/Buffering/Finished status of the video
3. Video Quality
4. Errors, reported by YouTube API
5. 10% increments of video played.
@a2sheppy, @teoli2003, @chrisdavidmills - what do you think? How much work would it be to go thru ~96-100 pages with YouTube videos and add `&enablejsapi=1&origin=` url params to them? Or should we make a KS template for including YouTube videos?