fixed multi-touch operation for both Windows and Android tablet

Users need three fingers when they want to move the WebGL 3D view by touch event so far.
But I combine the two operations, zoom-in/out and move, into one and now users need only two fingers.
In addition, behaviors of the domEvent attribute, "changeTouches", are different between Windows and Android tablets. That is why the operation "move" doesn't work in Windows-based tablets like Surface.
So I use the alternative attribute named "touches".