Add menu item custom field as suggest to http://shazdeh.me/2014/06/25/custom-fields-nav-menu-items/, discussion: http://wordpress.org/support/topic/have-installed-the-plug-in-but-dont-see-any-options

git-svn-id: http://plugins.svn.wordpress.org/menu-image/trunk@943322 b8457f37-d9ea-0310-8a92-e5e31aec5664