Add Frame Control for Page Hosting

[michael-hawker]

I've seen Pages mentioned for V1 of the standard, but I haven't seen their complement of Frame mentioned.

Frames seem like a pivotal navigation element to make use of pages for separating concerns within an application. They also allow developers to create a common shell/navigation context around their app with pages separating the concerns of individual application functions.

<Page x:Name="MainPage">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <TextBlock Text="Some Common Application Header/Branding Here"/>
        <Frame Grid.Row="1"/>
    </Grid>
</Page>

NavigationView (HamburgerMenu) uses a Frame for instance when the user clicks on an item in the menu to navigate to a separate experience in the main pane.