Gadget: Menu class
Bits: 0 - Set means entry is ticked.
1 - Set means entry has dotted line immediately below.
2-7 - Must be 0.
8 - Set means entry is faded.
9 - Set means entry is a sprite (text is default).
10 - Set means entry has submenu.
11 - Set means Menu_Submenu is raised when user traverses entry.
12 - Set means object to be shown from entry is shown with Wimp_CreateMenu semantics.
