Multitouch interaction and gestures

Changes the logic of gesture processing slightly. Originally, once a gesture was detected, VTK would continue processing it for all future mouse move (touch move) events until the finger was lifted or mouse was released. This is fine for single touch gestures but for multitouch gestures, it is typically required to switch to different gestures with different motions. For example, the user could touch the screen, start pinching and without lifting the finger, start panning. Another common interaction is when the user starts panning but the pointer math initially guesses the gesture to be a pinch gesture. Originally execution would be stuck processing pinch even if the user's fingers are performing a pan. This change would ensure that gesture recognition eventually matches up with the user's intention.