The following PR introduces improved support for Context api and other api's which wrap the root view.

## Context api
Navigation.registerComponent('navigation.playground.ContextScreen', () => (props) => (
  <TitleContext.Provider value={'Title from Provider'}>
    <ContextScreen {...props} />
  </TitleContext.Provider>
), () => ContextScreen);

## Redux
Navigation.registerComponent('navigation.playground.ReduxScreen', () => (props) => (
  <Provider store={reduxStore}>
    <ReduxScreen {...props} />
  </Provider>
), () => ReduxScreen);

## Plain Component - not changed
Navigation.registerComponent('navigation.playground.MyScreen', () => MyScreen);

This PR also upgrades the TypeScript version to 3.2.0 and RN version used in the playground app to 0.57.7

* New Android build flavor - `reactNative57_7`
* Unit test coverage is disabled, for some reason it broke after upgrading to RN 0.57.7

This commit also upgrades TypeScript to version 2.9.x

Unmount react views when bundle load completes

Users providing their own ReactNativeHost implementations should implement BundleDownloadListenerProvider
and make sure they set DevBundleDownloadListener when ReactInstanceManager.