Experimental gamepad support in r2047

[Pelinor]

Thanks gid15, gamepad support is wonderful. I have a suggestion to make the interaction even better: allow gamepads to be able to control save/load menus. (Up/down buttons to highlight the save and "X" to select and "O" to cancel.)

It could benefit keyboard users as well, but is especially useful to gamepad users who usually have their hands farther away from the mouse.