Added metrics for Video confidence
Merge branch 'master' of github.com:guardian/frontend into video-confidence

Conflicts:
	common/app/assets/javascripts/bootstraps/media.js
Add beacon which tells us how many videos started after the preroll started
Dodgy little println
Cleaned up some unneeded copy 'n paste
No need for that space
Merge pull request #5272 from guardian/video-confidence

Video confidence