Display MainGame.mnu and map in ordoor simultaneously

It's a complete mess for now - many things are out of place or shown
when they shouldn't be - and we can't move around the game map. But,
it's a good start.

internal/menus/menus.go

@@ -65,11 +65,16 @@ var TextOverrides = map[string]string{
 
 // FIXME: The menu is specified as type 2 (button) in these cases, which is
 // weird. Make it a menu for now.
+//
+// Hypothesis: MENUTYPE and SUBMENUTYPE are not equivalent?
 var TypeOverrides = map[string]MenuType{
 	"levelply:2": TypeMenu,
 	"savegame:2": TypeMenu,
 	"loadgame:2": TypeMenu,
 
+	// "thumb" is not a background.
+	"maingame:2": TypeStatic,
+
 	// ???
 	"configure_ultequip:7.5": TypeListBoxUp,
 	"configure_ultequip:7.6": TypeListBoxDown,