Implement a preference for enabling/disabling captions for embedded YouTube videos

See: https://issues.gpii.net/browse/GPII-3154

The enhancer should be able to manage the embedded YouTube videos through the iframe api to set the captions.

https://developers.google.com/youtube/iframe_api_reference

https://apple.stackexchange.com/questions/223380/how-to-configure-mobile-safari-to-show-closed-captions-on-videos-in-webpage
 
https://christianheilmann.com/2008/03/12/video-captioning-made-easy-with-the-youtube-javascript-api/
 
http://terrillthompson.com/blog/648