* Add a special target page option: None. Items with this target page will be unclickable, but will still react to hover events and so on.
* Extract missing item filtering as a separate method. 


git-svn-id: https://plugins.svn.wordpress.org/admin-menu-editor/trunk@941600 b8457f37-d9ea-0310-8a92-e5e31aec5664