Add a/b test for use sentry to monitor JS errors
Add sentry server details to env properties
Ensure sentry ab switch defaults to off
Merge branch 'master' into spike-sentry
Fix merge conflicts
Partial fix for grunt compile video js error
Merge remote-tracking branch 'origin/master' into start-pressing-draft
Update bower package for videojs to 4.6.3
Merge pull request #4732 from guardian/spike-sentry

A/B test to beacon JS errors to Sentry
Merge remote-tracking branch 'origin/master' into start-pressing-draft