Bug fixed: Unbind touch event when destroying the tooltip

Fixed touch event bug.

When tooltip is destroyed the touch event was not removed.
Added unbind to touch event to clear it,

The bind is done here:
// if this is a touch device, add some touch events to launch the tooltip
if ((this.options.touchDevices == true) ...) {
    $this.bind('touchstart', function(element, options) {
        object.showTooltip();
	});
}