Using a control as NavigationBar.Header or .HeaderIcon causes runtime exception

[gentledepp]

When using controls as header and heradericon like so:

  <NavigationBar.HeaderIcon>
        <PathIcon Data="{StaticResource list_regular}"
                  Foreground="{DynamicResource IconColor}" />
    </NavigationBar.HeaderIcon>
    <NavigationBar.Header>
        <Button Content="Header"
                Background="#00000000"></Button>
    </NavigationBar.Header>

and having a TabPage (which also shows them in its tab)

you get a runtime exception:

System.InvalidOperationException: The control Button (Content = Header) already has a visual parent ContentPresenter (Name = PART_ContentPresenter, Host = ContentControl) while trying to add it as a child of ContentPresenter (Name = PART_ContentPresenter, Host = TransitioningContentControl (Name = PART_Header)).

To mitigate this, I propose to introduce two additional properties:

• NavigationBar.HeaderIconTemplate
• NavigationBar.HeaderTempalte

You can then use these to setup your view like:

            .... 
             NavigationBar.Header="My Activities"
             NavigationBar.HeaderIcon="{StaticResource activity_regular}">

    <NavigationBar.HeaderIconTemplate>
        <DataTemplate x:DataType="StreamGeometry">
            <PathIcon Data="{Binding .}"  />
        </DataTemplate>
    </NavigationBar.HeaderIconTemplate>
    <NavigationBar.HeaderTemplate>
        <DataTemplate x:DataType="{x:Type system:String}">
            <TextBlock Text="{Binding .}" />
        </DataTemplate>
    </NavigationBar.HeaderTemplate>

and you're good to go.
As far as I understand, this should also be backward compatible.

PR is following! I hope you like it @OmidID :-)