Menu Customizer: update menus panel priority in preparation for mixed section/panel sorting coming soon to core. Menus will be placed after "Site Title & Tagline" and before "Colors"; because after site identity, navigation is the next logical component (considering the ability to completely manage navigation/menus in the customizer, rather than just changing theme locations).

git-svn-id: https://plugins.svn.wordpress.org/menu-customizer/trunk@964343 b8457f37-d9ea-0310-8a92-e5e31aec5664