* add back button to screens pushed to stack
* resolve tab icon from root screen, instead of first pushed screen
* omit components object from tabs

* Added bottomTabFontSize and bottomTabSelectedFontSize properties for android tab bar

* Added tabFontSize and selectedTabFontSize properties to the doc

* Fix default values of bottomTabFontSize and bottomTabSelectedFontSize properties.

For example, the following code will start a single screen app with two
screens pushed into the stack.

```js
Navigation.startSingleScreenApp({
    components: [
    {
      screen: 'example.Types',
      title: 'Navigation Types',
      overrideBackPress: true
    },
    {
      screen: 'example.Types.CustomButtonScreen',
      title: 'Custom Buttons'
    }
  ]
});
```

* Set titleBarSubTitleTextCentered as navigator style

- Adapt title center

* fixed false declaration

* Resolve default value through appStyle
* breaking - titleBarTopPadding is now dp instead of pixels

* v1.1.314 [ci skip]

* Added optional fixedWidth property to the Android side menu

- Fixes: https://github.com/wix/react-native-navigation/issues/510

* Added fixedWidth drawer param to te top-level-api doc

Resolve promise when startTabBasedApp and startSingleScreenApp complete.

* Add paddingTop to android ToolBar.

* Update documentation

* Add topTabTextFontFamily style option

* Add topTabTextFontFamily sample usage to example project

* add support to tell screen to place its self underneath the statusbar for android.

* added property to documentation.

This pull request allows you to disable the open gesture only in one side of the drawer.

```
Navigation.startSingleScreenApp({
      screen: initialScreen,
      drawer: {
        left: {
          screen: DRAWER_SCREEN,
          disableOpenGesture: false,
        },
        right: {
          screen: SIDEBAR_FILTER_SCREEN,
          disableOpenGesture: true,
        },
      },
    });
```

If we pass disableOpenGesture to the drawer root object, like this: 

```
Navigation.startSingleScreenApp({
      screen: initialScreen,
      drawer: {
        left: {
          screen: DRAWER_SCREEN,
          disableOpenGesture: false,
        },
        right: {
          screen: SIDEBAR_FILTER_SCREEN,
          disableOpenGesture: true,
        },
        disableOpenGesture: true <======
      },
    });
```

Then the two drawer positions would be gesture disabled and the specific disableOpenGesture would be ignored. This way we don`t introduce breaking changes.

Fix props loading from PropsRegistry in custom buttons

This reverts commit e69f3801b9.

This fix allows to pass unserializable props to custom buttons, such as navigator or functions.

* Support showing modals with the default screen push/pop animation

* Set navigation bar color before modal is displayed

* Implement screenAnimationType property

controls animation type of all screens including modals.

Until now, buttons would use the same font family used by the title,
this commit introduces navBarButtonFontFamily property which allows to set
a different font family for title and buttons.

* Support subtitle FontFamily on size on Android

Font family can be either a .ttf/.otf asset or one of the default font families:

* sans-serif (regular)
* sans-serif-light
* sans-serif-condensed
* sans-serif-thin
* sans-serif-medium

* update docs

This commit adds support for fade and slide-horizontal animations for modals and a few other animation related changes:

* Support defining animationType when calling dismissModal
* Support fade and slide horizontal animations for modals
* Slightly reworked current screen animations timings
* Fixed slide-horizontal x offset and removed alpha

Ability to set a flat border under the TopBar. `topBarElevationShadowEnabled` should be set to true if using this feature.

* testing

* test

* try fix props on topTabs

* Test xml menu

* Add titleBarHeight

* Remove test

* Add to StyleParams

* Add topTabsHeight

* Fix styleParams type

* Add navBarFontBold

* Add typeface package

* Remove unused debugging

returns true if NavigationActivity is resumed (startApp was called)

* added method for getting the currently visible screen ID. Can be useful to decide if logic should be applied according to screen visibility, for example: set buttons/title dynamically, or even determine that you don’t need to show the same screen again if it’s the current one that’s showing

* Implement getCurrentlyVisibleScreenId on Android

Can be used statically:
Navigation.getCurrentlyVisibleScreenId() - returns the unique screen
instance id

With a navigator instance:
await this.props.navigator.screenIsCurrentlyVisible() - resolves a
promise that checks if the current screen is visible

* Add screen visibility listener which can be registered globally

API
new ScreenVisibilityListener({
    willAppear: ({screen, timestamp}) => console.log(`Displaying screen ${screen}`),
    didAppear: ({screen, timestamp}) => console.log(`Screen ${screen} displayed in ${Date.now() - timestamp} millis`)
  }).register();

todo
* Add timestamp to modal, resetTo
* implement unregister
* implement iOS

* Add global screen visibility listener to example app

* Think I better assign a value to emitter

* Send timestamp in resetTo

* Moved listener to library, it can be deleted from the app

* Add push and resetTo buttons to pushed screens

* Send appear/disappear events after animation ends

* Pass pop timestamp from js

* Send timestamp in popToRoot

* Add popToRoot button in push screen

* Add few navigation buttons to modal screen

* Pass timestamp to tabs

relevant only to first/initial tab

* Update timestamp when navigating between BottomTabs

* Send screen visible events after modal dismiss

* log willDisappear and didDisappear

* Report both start and end timestamps

* Implement unregister

* Send NavigationType parameter in visibilityEvent

This indicates the type of the navigation command that triggered the visibility change

* Rename pushInitialScreen to more explicit name

* Fix duplicate initialScreen visibility events

* Update screen visibility log statement

* Show popToRoot in modal screen only if screens were pushed

* implement global screen event for iOS

* fix lint issues

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

* 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

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({ ... });
}

* Added tapBackgroundToDismiss to LightBox screens

* Updated LightBox readme

* Formatting updates

* Fixed ios selector

* Updated animationEnd hide method

Change bottom tab bar button image at runtime

Usage is identical to switchToTab, closes #842

This commit adds support for the following style properties:
titleBarTitleFontFamily - string, font name in assets
titleBarTitleTextCentered - boolean, default is false