Translucent ios nav bar

Looks like translucent not work correctly on iOS, I'm change in `ReactNavigationImplementation.swift` method `reconcileScreenConfig` part with translucent config to:
```
if let translucent = boolForKey("translucent", next) {
if (translucent == true) {
navBar.setBackgroundImage(UIImage(), for: UIBarMetrics.default)
navBar.shadowImage = UIImage()
navController.view.backgroundColor = UIColor.clear
}
navBar.isTranslucent = translucent
}
```
but I really don't know how disable it when next screen will be with translucent false

Start in ReactNavigationImplementation.swift at reconcileScreenConfig and inspect how the translucent navigation-bar configuration is applied when screens change. Reproduce transitions between translucent and non-translucent screens on iOS; the work is done when both states render correctly across navigation changes.

Written by the indexing model from the issue text.