BackgroundView stays highlighted even when gesture gets cancelled

[mickeyl]

This is a problem, e.g. when using the new multitasking feature on the iPad Pro. The proper fix seems to me:

 - (void)handleGesture:(UIGestureRecognizer *)recognizer {
-    [self setBackgroundVisibility:!(recognizer.state == UIGestureRecognizerStateEnded)];
+    [self setBackgroundVisibility:!(recognizer.state == UIGestureRecognizerStateEnded || recognizer.state == UIGestureRecognizerStateCancelled)];