ScrollingNavigationController.updateNavbarAlpha steps on third party toolbar buttons

updateNavbarAlpha hammers the alphas of all subviews of everything on the toolbar, including some third party libraries we use that do special things with their toolbar buttons.

the specific problem is the nested function:
```swift
func setAlphaOfSubviews(view: UIView, alpha: CGFloat) {
view.alpha = alpha
view.subviews.forEach { setAlphaOfSubviews(view: $0, alpha: alpha) }
}
```

the easiest solution would be to make this function a public function instead of nested function inside a private function, so we could just override the behavior with our own logic.

otherwise adding a property ScrollingNavigationController to exclude button subviews by name or class would be needed.