Fix broken link and mention the new redux example project.

This reverts commit 685009bc23.

When selected tab changes - change visibility instead of adding and removing views from hierarchy

Related to #2892

To use it, Override `createReactNativeHost` in MainApplication as follows:

```java
    @Override
    protected ReactNativeHost createReactNativeHost() {
        return new NavigationReactNativeHost(this) {
            @Override
            protected UIImplementationProvider getUIImplementationProvider() {
                return new SyncUiImplementation.Provider();
            }
        };
    }
```

This commit also changes the way TopBar background color is applied.
Instead of applying it to the TitleBar, it's applied to the entire TopBar layout

The links were pointing to the wrong documentation sections.

This option allows to control when tab titles are displayed

* showWhenActive: when a tab is focused
* alwaysShow: show regardless of which tab is in
* alwaysHide: never show tab titles

This commit also changes the way TopTabs options are handled. As the TabLayout
is part of the TopBar, it's the StackControllers responsibility to set TopTabs options.

Hopefully increasing button size will eliminate flakyness

* V2: Peek and pop

* Add event when preview is dismissed in non commit mode

* tslint

* Refactor playground. Document preview api

* Added width prop

* Implement hybrid push/preview button

* Fixing small linting errors

* Testing new multi pr job

* Disable unmounts when dismissed

This works around an issue with RN's view reconciliation when the
root component has no background color defined.