Add a way to select a construction option upon opening a menu

[GoogleFrog]

threxxy wants to select Radar when he presses V to open the Special menu. This is pretty easy, since menu opening hotkeys are already handled in KeyPressed rather than as a generic action. The tricky part is making this configurable. Perhaps make a submenu of radio buttons, one set for each menu, with options corresponding to build options. The integral menu config does not seem to be set up to report the required information to the widget nicely.