Menu Customizer: first pass at ajax to submit new-menu creation. New menus can now be created, but not all features work as they should after the menu is added to the page as a new dynamically-added section.

git-svn-id: https://plugins.svn.wordpress.org/menu-customizer/trunk@943191 b8457f37-d9ea-0310-8a92-e5e31aec5664