Metadata for audio and video files:

* Make attachment metadata for audio files editable by providing a metabox on the Edit Media page
* Standardize on using the attachment title everywhere
* Label the Caption and Description fields for audio and video appropriately
* Make the playlist Underscore templates more straightforward

See #27574.


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git-svn-id: http://core.svn.wordpress.org/trunk@27693 1a063a9b-81f0-0310-95a4-ce76da25c4cd
In `wp_generate_attachment_metadata()`, when an audio or video files contains upload-able image bits in its ID3 tags, only upload it if the image has not already been uploaded. Determine this by checking for a `_cover_hash` value in post meta that matches the `md5` representation of the bits.

This prevents uploading an album of 10 songs and subsequently uploading 10 copies of the same album cover.

Props GregLone for the new filter/filter docs: `'attachment_thumbnail_args'`.
Fixes #27573.
 

Built from https://develop.svn.wordpress.org/trunk@27863


git-svn-id: http://core.svn.wordpress.org/trunk@27694 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Cleanups for audio/video metadata, see [27862].

see #27574.

Built from https://develop.svn.wordpress.org/trunk@27864


git-svn-id: http://core.svn.wordpress.org/trunk@27695 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Using percentages for playlist font-sizing was ambitious, but fell prey to `editor-style.css` in the admin. We have switched to using pixels. The editor styles were also forcing MediaElement players to inherit `font-family`, which was undesirable. And while we're at it, remove the top and bottom border from the playlist's list of tracks, which adds a dash of lovely to the playlist's default styles.

Props nacin for the addition of `&mdash;` in the playlist track list.
Fixes #27600.


Built from https://develop.svn.wordpress.org/trunk@27865


git-svn-id: http://core.svn.wordpress.org/trunk@27696 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Use correct formatting function. see [27864], see #27574.

Built from https://develop.svn.wordpress.org/trunk@27866


git-svn-id: http://core.svn.wordpress.org/trunk@27697 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Bump the MediaElement version in `script-loader.php` to `2.14.1`.

See [27861].


Built from https://develop.svn.wordpress.org/trunk@27867


git-svn-id: http://core.svn.wordpress.org/trunk@27698 1a063a9b-81f0-0310-95a4-ce76da25c4cd