Improved support for fallback recognizers

After running into some issues with conflicting gesture recognizers, I've extended the `- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldReceiveTouch:(UITouch *)touch` method to disregard touches that would otherwise only be disregarded when the `- (void)handlePanGesture:(UIPanGestureRecognizer *)gesture` method gets called. By disregarding these touches earlier, other gesture recognizers will be able to detect the "failed" gesture and respond accordingly.