fixes #1502

This reverts commit 6f7f9d1986.

This reverts commit 918d7859c1.

* fix images name

* upgrade example project to rn51 - ios

When disabling elevation by setting topBarElevationShadowEnabled to false, this commit allows to re-enable it by setting the same property to true.
Elevation was previously disabled by using setOutlineProvider(null), with ViewOutlineProvider being an Android 5.0+ object responsible for determining how views draw their outline. To allow re-enabling elevation, we keep our original ViewOutlineProvider and restore it when elevation is enabled again.

* Document how to use index.js as entry point (ios)

* android too

* android too (fixed)

* Revert "Improve getCurrentlyVisibleScreenId on iOS with drawers. (#2052)"

This reverts commit 2c30a52bb9.

* Revert "introducing navbar shadow on iOS (#2339)"

This reverts commit 8fd496e0c9.

* Revert "This fixes an issue with a custom title-view (which has a title and a subtitle) appearing at the left side of the nav-bar instead of the center during a transition animation: when a screen with this title-view is being pushed or when you pop back to it. (#2384)"

This reverts commit 3f7f6c2612.

* Revert "Now allowing the custom nav bar to take up the whole space on iOS (#2306)"

This reverts commit 74a02ccfc5.

* adds shadow opacity, shadow color, shadow offset, shadow radius to navbar for ios

* mentions ios shadow in styling-the-navigator docs

This happens because the title-view is being created again when RVVViewController appears. There's probably no point in setting the title-view again with the same data when it already has it. The title view setup is done anyway in RCCNavigationController.

This can be easily reproduced by calling "this.props.navigator.setSubTitle({subtitle: 'a subtitle'});" from the constructor of a pushed screen.

* Now allowing the custom nav bar to take up the whole space on iOS

- Also the custom nav bar reacts well to orientation changes
- Fixes: https://github.com/wix/react-native-navigation/issues/1893

* It now works well on iOS 11 as well

* v1.1.314 [ci skip]

* Added optional fixedWidth property to the Android side menu

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

This code block appears fine on GitHub, but is malformatted on the site. This commit updates it to fit the format of other code blocks in the docs, so it should appear okay.

* 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

* 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.