Main Menu and User Menu within admin section

[HostOncilla]

It would be really good if we could manage the main menu and user menu within the admin section. We could rearrange menus and submenus, add extra menus and submenus, add icons to the menus and submenus, overwrite links for the main menus and seubmenus, and so on. For the user menu, we could rearrange and add icons to it.