New CSS and screen size to allow better positioning.

Image is now behind the cub monitor instead of surrounded by it. I've
fiddled about a bit and tweaked the visible portion to match
photographic evidence, and to get Boffin working (fixes #26).

Elite looks a lot better too.
allow custom keycode mapping in URL eg ?KEY.LEFT_SQUARE_BRACKET=AT
allow mapping of Gamepad buttons in URL, eg
?GP.LEFT1=CAPSLOCK&GP.RIGHT1=CTRL&GP.A=RETURN&disc=%7CAardvark%2FZalaga.zip&autoboot
just formatting
Reinstate tests accidentally deleted in earlier checkin
Fix up the aspect ratio
More aspect ratio tweaking (thanks @murkle)