Added a missing curly bracket in top tabs example.

fixes https://github.com/wix/react-native-navigation/issues/1771

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

* Add support for react-native 0.52.0

* Refactore a bit

1. Rename `DevCommandsHandlerProxy` to `DevHelperProxy` so it reflects the changes in RN. See d19afc73f5 .
2. Add few comments to show which code is used on `RN >= 0.52` and which on `RN <= 0.51`.

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

The custom nav bar on iOS was really just a custom view applied to the title of the navigation bar.
There were problems with this approach, because the navigation bar messes up the frame of the title very frequently, especially when the orientation is changing. That behaviour is accepted when the title is a label, but not when we have a custom component.

With this pull request the custom nav bar component can take up the full width of the navigation bar, no matter what orientation we're at.

* Added mix of native btns and custom component on the Custom TopBar screen of the example project

The initial modal screen got animated twice, this regression was introduced in #2761.

* 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'
    }
  ]
});
```

* Refactor resetTo view controller creation into function

This will allow for multiple view controllers to call the same function to create their instance.

* Configure resetTo to take multiple components to set view controllers for

This allows for a navigation stack to be recreated with multiple view controllers rather than just one.

* Breakup view controller initializer into multiple lines for legibility

* Set titleBarSubTitleTextCentered as navigator style

- Adapt title center

* fixed false declaration

relates to #2711

fixes #2711

This reverts commit 90b47f7910.

Apparently runOnPreDraw is not enough anymore, possibly broke in RN 0.51

Support for react-native 0.52.0

Rename `DevCommandsHandlerProxy` to `DevHelperProxy` so it reflects the changes in RN. See d19afc73f5

Otherwise, if the users sets custom insets (additional insets), they override the system adjusted insets. This is not the expected behavior.