Twenty Thirteen: first pass at RTL CSS and JS support. Props DrewAPicture and maor, see #23550.

git-svn-id: https://core.svn.wordpress.org/trunk@23643 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Thirteen: RTL JS support, fix class selector, see #23550.

git-svn-id: https://core.svn.wordpress.org/trunk@23644 1a063a9b-81f0-0310-95a4-ce76da25c4cd