* Add topTabTextFontFamily style option

* Add topTabTextFontFamily sample usage to example project

* Preview API

* Added preview actions and fail-guard wrappers

* Remove old setters

* Moved from passProps to actionParams

* Move findNodeHandle to internal method

* Removing findNodeHandle

* Added height and option to dont 'pop' the view controller

* Documentation update for peek and pop

* Document how to access button press events

* Commit by default in example. Because it's cool

* Docs and if elses ifs then

* Unregister previous ViewController on attempt to preview.

* Merge conflict fail

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

* added property to documentation.

Missed Comma throw "unexpected Token" error.

This reverts commit 076ee7311e.

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

iOS update style-update rutine to update each viewcontroller in a NavigationViewController
tabButtonColor improvement

* Add converter for UIBarButtonSystemItem

* Add support for UIBarButtonSystemItem-styled buttons

* Add documentation about systemItem

* 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' }],
    }],
 })
/>
```

This commit saves navBar component props in propsRegistry and restores the saved props
when the component is mounted, allowing us to pass unserializable props to custom navBar component.

This fixes a bug where navigator-level styles could override styles on a specific button.

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.

This reverts commit 9f2f15bc4f.

* Support iOS 11 prefersLargeTitles #1643

* better and more simple version checking and setting

This commit applies the save props mechanism used when pushing screen
to navigator buttons as well, enabling us to pass unserializable props to buttons.

* throwing an error instead of a string

* return a callback to remove the register handler

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.

fixes #2166

This commit adds ability to register multiple navigator event listeners:
navigator.addOnNavigatorEvent(func)
navigator.removeOnNavigatorEvent(func)

Event listeners are removed when the screen the navigator is bound to
is unmounted, calling `removeOnNavigatorEvent` isn't mandatory.

As this api conflicts with the current api, addOnNavigatorEvent can't be used
in a screen where setOnNavigatorEvent was used before.

On some devices, when returning to the app from background, some launchers
open the SplashActivity over the NavigationActivity. In this case, simply finish the SplashActivity
and return the the preview NavigationActivity.

This is potentially a breaking change as calling navigator.switchToTab()
won't do anything now if the current tab is already selected.

closes #2143

No major changes, just tweaked values a little bit.

* Fab animation duration changed to 120 (previously 200)
* Fab show animation: Scales from 0.6 to 1 (previously 0)
* Fab hide animation: Scales from 1 to 0.6 (previously 0)
* Removed alpha delay from screen animation
* TranslationY value changed from 8% to 5%