* Adjust submenu icons so that they line up perfectly with top-level menu icons. Can't come up with anything better at this time.
* Do not show icons on submenu separators, it looks wrong.
* When the "Show submenu icons" setting is "only when manually selected", do not show default submenu icons in the editor. That is, the icon URL still shows up, but the icon itself does not.
* Add a hover effect to image-based submenu icons. It's basically a copy of the hover effect that WordPress uses for top level menus.

git-svn-id: https://plugins.svn.wordpress.org/admin-menu-editor/trunk@940794 b8457f37-d9ea-0310-8a92-e5e31aec5664