Leap motion, finally

Only 2 gestures are supported: swipe and circle gesture. Circle gesture calls nextscreen, swipe - left, right, bot right, bot left, bot, etc... 
Works quite good. Not sure how usable is it, but it's fun.
There are others gesture types: key tap and screen tap. ScreenTap might be useful, it returns the screen user tapped on and the coordinate of the tap. I am not sure how to integrate into ShiftIt.
It is promised that the new gestures will arrive with LeapSDK update, so I might add them in future.

I am using hardcoded strings for calling - (void)invokeShiftItActionByIdentifier_:(NSString *)identifier. Might be a good idea to create const instead.