UX Changes:
* Don't add a menu item for "Add Audio|Video Source"
* In the Audio|Video Details modal, add buttons and some suggestive text for adding alternate playback sources
* Don't show "Create Audio|Video Playlist" menu items until the user has uploaded audio or video files
See #27437.
Built from https://develop.svn.wordpress.org/trunk@27608
git-svn-id: http://core.svn.wordpress.org/trunk@27451 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Scott Taylor