DFW: restore editor width shortcuts, restore limited overwriting of the theme...

DFW: restore editor width shortcuts, restore limited overwriting of the theme styling in TinyMCE, show the toolbar on mouse move in TinyMCE, improve the help, fixes #17503, fixes #17644, fixes #17664, fixes #17596

git-svn-id: https://core.svn.wordpress.org/trunk@18137 1a063a9b-81f0-0310-95a4-ce76da25c4cd