This is working on the screen API too, however it's not included in screen API, only on top-level screen

* setTabButton -> has now the property 'label' to change the label of the TabButton

* Add to documentation

* [BugFix] use i instead of 0 to check all TabItems

Add the preview and pop feature

To use the feature you simply call `navigator.push()` but with additional parameter `previewViewID` which is a React Node.

```js
<TouchableOpacity
  onPressIn={() => this.props.navigator.push({
    screen: 'screenid',
    previewView: this.viewRef,
    previewActions: [{
      title: 'Foo',
      style: 'selected', // none, selected, destructive
      actions: [{ title: 'Bar' }],
    }],
 })
/>
```

* throwing an error instead of a string

* return a callback to remove the register handler

* 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

* Add missing parameter instruction for in app notification

* Merge changes as origin master

* add adjust soft input optional config for Lightbox on android platform

* Add doc about adjustSoftInput for showLightBox

* Remove extra line-break to fix rendering list in doc site.

* Add In-App Notification

* [iOS] Added fade transition animation between screens

* Update docs for #1367

* setDrawerEnabled with params side and enabled

* Tweak docs, small RCCDrawerController fix

* Correct indents

* Correct indents

* Fix documentation website link

* Update docs

Add setSubTitle implementation for iOS + docs

Fix dead link

* Initial commit

* Initial commit

* Clean-up title