apps/graphics/twm4nx: Replace most usage of NUL-terminated C strings with NXWidgets::CNxString.
apps/graphics/twm4nx: Add initial support for the main menu. The main menu will come up when a left click is performed on the background. The main menu is used for starting applications. The adds the CMainMenu class that implements the main menu and an IApplication interface class the provides th template for how any external C++ application can add itself to the Main Menu.
Still missing is the logic that responds to the meny item selection and sends the event to the Main Menu as well as the logic in the Main Menu that handles the event and either brings up a sub-menu or starts and application.
Things are still basically functional after these changes, but my gut feeling is these changes added some instabilities that will need to be smoothed out.
