Issue title: XamlNavigation\NavigationMenu Windows Platform sample have a design-time preview
 Issue body: The XamlNavigation\NavigationMenu sample's SplitView menu on AppShell.xaml only hallandrew@example.com.    In the design-view in VS 2015 I can see the hamburger menu/togglebutton but no content from the icons and menu item labels.

Anyone know if this is a bug or this implementation doesn't provide a design-time view?

Thanks,
 Rick
 Comments: 
 Comment 0: @rickengle, thank you for your feedback. The navigation items are created in code-behind and added at run time. It's expected that the items are not available in design view.
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