Haptic player should only vibrate when a finger is onscreen.

[hugofloresgarcia]

Right now, the haptic player is always active, and will always vibrate at the amplitude of the haptic pixel located at the center of the screen. The desired behavior, instead, is to have the haptic player activate only when the user is scrolling. Maybe we should tie a gesture to the scrollview that tells it to activate the haptic player only when the scroll gesture is activated?