Implemented GoBackCommand for Windows app.
The light mode does now app-wide applied.
Avoid multiple registering of application settings.
Add Windows.UI.ApplicationSettings to the using directives of MainPage.xaml.cs and clean up the code.
Add virtual methods to basicPage.cs for overriding.
Add more content to the PageState in WP and Windows.
Remove non-working and useless code from MainPage.xaml.cs