* add basic contributing guidelines to docs

* some English and formatting

* Add badges to README.md

* docs - how to run on android

* markdown formatting

* Add troubleshooting of old node

* Fix formattting

* Fix markdown and troubleshooting

relates to #1555

Usage:
    navBarCustomView: 'example.CustomTopBar', // registered component name
    navBarComponentAlignment: 'center' // 'center'/'fill'

* add v2 link to readme

* Update README.md

* Add font family support on bottom tabs

* import missing classes

* import missing class

* update document

* Support customize icon for left nav button in android

* Add navBar navBarTextFontSize support for android

* #1071 Test that Navigator forwards NavigationOptions to ViewController

* Add an argument allowing to run a single Android e2e test

* Fix style issue

* #1071 Allow changing navigation title in iOS

* Update readme to document an option for running a single test

* Update ScreenStyleDynamic.test.js

* Upgrade Gradle version

* Allow playground app to run on x86_64 emulator

* #1071 Allow changing navigation title

* #1071 Add tests for JavaScript

This reverts commit 36d2c7e35c.

This uses the proper methods for instantiating the initial view on iOS.
By utilizing these methods, we can stand up the initial view controller
from the storyboard.

See also:
https://developer.apple.com/library/content/documentation/General/Reference/InfoPlistKeyReference/Articles/iPhoneOSKeys.html#//apple_ref/doc/uid/TP40009252-SW41

[iOS] Added ability to set static(root) background image

Currently startApp is called from global context which results in the
app being launched when headlessJs tasks run in the background.
In order to support this use case, while not breaking existing users,
this commit adds two mechanisms which should help users detrmine if
the native Activity is running and startApp can be called safely.

1. RNN.appLaunched event is emitted is SplashActivity starts and react
   context has already been created. This is the use case of openeing
   the app while headless js task was started or has just finished and
   react context is in a "pasued" state.

2. Navigation.isAppLaunched() convenience method has been added.
   It returns a promise which when resolved, indicates if the app
   is launched and we should show the ui or not.

Usage

import {Navigation, NativeEventsReceiver} from 'react-native-navigation';

Promise.resolve(Navigation.isAppLaunched())
  .then(appLaunched => {
    if (appLaunched) {
      startApp();
    } else {
      new NativeEventsReceiver().appLaunched(startApp);
    }
  });

function startApp() {
  Navigation.startTabBasedApp({ ... });
}