message: Removed handling of change from/to system item
  This is handled by BarButton component setting its key to system item
diff: @implementation NVBarButtonView
  {
  __weak RCTBridge *_bridge;
  - NSString *_title;
  NSString *_testID;
  - UIImage *_image;
  }
  - (id)initWithBridge:(RCTBridge *)bridge
  - (void)setTitle:(NSString *)title
  {
  - _title = title;
  self.button.title = title;
  }
  if (!!source) {
  [[_bridge moduleForName:@"ImageLoader"] loadImageWithURLRequest:source.request size:source.size scale:source.scale clipped:NO resizeMode:RCTResizeModeCover progressBlock:nil partialLoadBlock:nil completionBlock:^(NSError *error, UIImage *image) {
  dispatch_async(dispatch_get_main_queue(), ^{
  - self -> _image = image;
  self -> _button.image = image;
  });
  }];
  } else {
  - _image = nil;
  _button.image = nil;
  }
  }
  {
  if (systemItem != NSNotFound) {
  self.button = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:systemItem target:self action:@selector(buttonPressed)];
  - } else {
  - self.button = [[UIBarButtonItem alloc] init];
  - self.button.style = UIBarButtonItemStylePlain;
  - self.button.target = self;
  - self.button.action = @selector(buttonPressed);
  - self.button.image = _image;
  - self.button.title = _title;
  self.button.accessibilityIdentifier = _testID;
  }
  }
  