Add stack navigation using navigation stub from Create app

[Yajur-Grover]

Gallery uses the react-navigation community module to navigate between different pages. As it is not a core component, an alternative solution will need to be found on the Fabric version of Gallery.

Currently, there is no real form of navigation present on the test app - in order to view a different example page, the user needs to manually change which example page is being displayed on the homepage from the editor. The next step from this is to implement stack navigation, using this navigation stub from the Create app.