Add TinyMCE placeholders for `audio` and `video` shortcodes.

* Add `wp.media.mixin`.
* Add `wp.media.audio` and `wp.media.video`.
* Add `wp.media.model.PostAudio` and `wp.media.model.PostVideo`
* Add `wp.media.controller.AudioDetails` and `wp.media.controller.VideoDetails`.
* Add `wp.media.controller.ReplaceAudio` and `wp.media.controller.ReplaceVideo`.
* Add `wp.media.view.MediaFrame.AudioDetails` and `wp.media.view.MediaFrame.VideoDetails`.
* Add `wp.media.view.AudioDetails` and `wp.media.view.VideoDetails`.
* Update the `wpgallery` TinyMCE plugin.
* Display audio and video players in the media modal when shortcode is clicked.
* Provide a UI to edit shortcode attributes in the media modal.
* Provide a UI to replace the `src` media file in an `audio` or `video` shortcode.

See #27016.



git-svn-id: https://develop.svn.wordpress.org/trunk@27411 602fd350-edb4-49c9-b593-d223f7449a82