TinyMCE: update to 4.0.16, see #24067.

git-svn-id: https://develop.svn.wordpress.org/trunk@27062 602fd350-edb4-49c9-b593-d223f7449a82
Let the video shortcode accept a YouTube URL as the value of its `src` attribute, as MediaElement.js supports Chromeless YouTube videos by using a pseudo-mime-type `video/youtube`. 

HTTP and HTTPS www, non-www, and short url fronts are supported:
http://www.youtube.com/watch 
https://www.youtube.com/watch
http://youtube.com/watch
https://youtube.com/watch
http://youtu.be
https://youtu.be

Fixes #24764.



git-svn-id: https://develop.svn.wordpress.org/trunk@27063 602fd350-edb4-49c9-b593-d223f7449a82