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

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({ ... });
}

This fixes issues with other React Native views which rely on the view controller hierarchy.

* Move logic for tap background to dismiss out of background color view

This allows for tapping the background without setting a color here, meaning this feature can be enabled with one less view in the view hierarchy

* Only allow taps on views that aren't the React view

This allows for taps on any background view, visual effect view, color tint view, etc, but not on the content.

Yarn apparently still has issues with relative paths.

OCD made me do it.

* Added tapBackgroundToDismiss to LightBox screens

* Updated LightBox readme

* Formatting updates

* Fixed ios selector

* Updated animationEnd hide method

added a missing comma in the 'style object format' so to help users who copy/paste this code block

Fixes #1411
Each time a color attribute is set in AHBottomNavigation, all items in
the BottomTabs are recreated. If a badge is set, it is animated each
time items are recreated. This behaviour can even be seen in the gifs
in the repo https://github.com/aurelhubert/ahbottomnavigation

* Fixed lightbox status bar color override on Android

* Added missing imports

added 03d380f8a9 back and also applied this fix https://github.com/wix/react-native-navigation/issues/428#issuecomment-278268928 on top of it

Removing duplicate property

React is now migrating away from React.PropTypes starting from v15.5.0
More info:
https://facebook.github.io/react/blog/2017/04/07/react-v15.5.0.html

Can be null if returning from another app and our activity wad destroyed in background