Sub menus fully working.

- Sub menus close when clicked
- Additional function added to handle sub menu clicks (like 'Quit)
- Commented out color change of sub menus since they close immediately
when clicked
- No phantom clicking of sub menus now (yeah!) without a main menu item
being clicked first
Installed gtkmm for file dialog.partially working

- Compiles okay, but given an error when exiting from 'Release' mode
- Debug seems okay
- Ready to start adding actual gtk code...I think