TinyMCE:
- Update the styling of the image caption and gallery toolbars.
- Fix issue where the hidden clipboard div in wpView.
- Switch to using the pencil dashicon for Edit.
- Add `max-width: 100%;` to images in the gallery preview and adjust column widths.
Props cramdesign, mattheu, gcorne, melchoyce, see #27320, fixes #27376, fixes #27354

Built from https://develop.svn.wordpress.org/trunk@27578


git-svn-id: http://core.svn.wordpress.org/trunk@27421 1a063a9b-81f0-0310-95a4-ce76da25c4cd