Swipe handling. Swipes trigger arrow key presses.

Not sure that this is worthwhile now that the click on the map stuff is in there but it's done now so if you want it...

I put it in the engine (rather than the world), so the swipes could be easily used for other actions.

Does include 18kb of (un-minified) js - jquery.event.move.js and jquery.event.swipe.js