Menu Customizer: change WP_Menu_Customize_Control::type and the associated settings' types to `nav_menu`. Outline (in pseudo-code) the process for saving (publishing) menu updates and re-ordering.

git-svn-id: https://plugins.svn.wordpress.org/menu-customizer/trunk@942480 b8457f37-d9ea-0310-8a92-e5e31aec5664