Fix TinyMCE Views in IE8 and 7:
- Add fallback background images for dashicons.
- Fix hiding the clipboard while still allowing the contents to be selected.
- Work around lack of border-box in gallery styles.
(Includes precommit cleanup for theme.js)
Props gcorne, fixes 27546

git-svn-id: https://develop.svn.wordpress.org/trunk@28062 602fd350-edb4-49c9-b593-d223f7449a82