title: UIView animation getting paused when another UIViewController is presented
body: <p>I have a <code>UITabBarController</code> as the rootViewController for my app. When a download is initiated I show a badge on my last tab and have it pulse colors to show that a download is happening:</p>
  
  <pre><code>- (void)incrementBadgeValue {
  
      UITabBarItem *moreTabBarItem = [self.tabBar.items lastObject];
      moreTabBarItem.badgeValue = @"↓";
  
      self.originalColor = moreTabBarItem.badgeColor.copy;
      UIColor *toColor = [UIColor darkGrayColor];
      NSTimeInterval duration = 1.5f;
  
      [UIView animateWithDuration:duration
                            delay:0.0
                          options:UIViewAnimationOptionAutoreverse | UIViewAnimationOptionRepeat | UIViewAnimationOptionCurveEaseInOut
                       animations:^{
  
                           moreTabBarItem.badgeColor = toColor;
  
                       } completion:^(BOOL finished) {
                           if (finished) {
                               moreTabBarItem.badgeColor = self.originalColor;
                           }
                       }];
  
  }
  </code></pre>
  
  <p>This works great, until another <code>UIViewController</code> is presented over the window, or the user leaves and returns to the app. In these cases the animation is paused/stopped.</p>
  
  <p>How can I continue this animation in this case?</p>