Menu Customizer: use a JS template for the Nav Menu control. This will be especially useful when menu-addition is made fully dynamic, as new menus can have associated controls instantiated entirely via JavaScript. Also rename the menu and menu item controls to be more consistent with WordPress core's naming conventions. 

git-svn-id: https://plugins.svn.wordpress.org/menu-customizer/trunk@1039703 b8457f37-d9ea-0310-8a92-e5e31aec5664