A MenuList is a specialised list subclass for holding Menu instances, for use as the menus
property of an Application or Window. It provides ways of finding menus
and menu items by command name, which allows you to modify the standard
menus without making platform-specific assumptions about their layout.
- Returns the Menu containing the item with the specified command name, or None if there is no such menu.
- Returns the MenuItem having the specified command name, or None if there is no such item.