TinyMCE: add support for IE11.
- Add the latest changes from the 3.x branch upstream.
- Reduce the number of calls to tinyMCEPopup.restoreSelection() in our custom plugins.
- Remove the deprecated execCommand("mceBeginUndoLevel");.
See #25281.
Built from https://develop.svn.wordpress.org/trunk@25748


git-svn-id: http://core.svn.wordpress.org/trunk@25661 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fourteen: merge recent stylesheet changes to RTL, and file miscellaneous CSS cleanup.

RTL still needs more responsive fixes, see #25332 -- and a11y menu fixes, see #25054. 
Built from https://develop.svn.wordpress.org/trunk@25749


git-svn-id: http://core.svn.wordpress.org/trunk@25662 1a063a9b-81f0-0310-95a4-ce76da25c4cd