Added support for ST NavigationView component

Adds new overrides for the 'st.navigation.View' and 'st.navigation.Bar' components.

View supports the 'defaultBackButtonText' config property.
Bar attempts to keep the back button text and the titles of any views in the stack updated.

Updated index.js with examples of the new functionality - third tab now houses the navigation view, bottom toolbar has a new button to add new views to the stack.

Updated the content files with appropriate text for the new examples (french translations courtesy of google).