Improved controller support in menus

Better support for usb controllers has been added in particular for the load/save dialogs and in game difficulty prompts. Most actions can now be done with the controller with the exception of volume control and some settings.

Improved the look of the dialogs

Improved the handling of the small Needle ship by adding an acceleration factor before it gets to full speed. Makes a huge difference to playing with ship and I'm pleased I noticed it needed improving before release.