title: Horizontal / Vertical Alignment Not Working in RelativePanel
body: <p>I am trying to create a <code>RelativePanel</code> (for reflow purposes) with two <code>Image</code>'s and a <code>StackPanel</code> in it. When in a "small screen" view, I want it to lay out vertically in a column: <code>Image</code>, <code>StackPanel</code>, <code>Image</code>. It does this just fine, but the problem is that the <code>StackPanel</code> has a height of 0, so the bottom <code>Image</code> is smack up against it. I want the <code>Image</code> to snap to the bottom of the screen. However, <code>VerticalAlignment="Bottom"</code> refuses to work. After a little more testing, I've found that <code>HorizontalAlignment</code> doesn't work, either. Does aligning not work properly in a <code>RelativePanel</code>? Or is there a special way to do it?</p>
  
  <p>Here is the full XAML:</p>
  
  <pre><code>&lt;RelativePanel&gt;
      &lt;Image Width="100" x:Name="AppleImage" Source="/Assets/Images/apple.png" Margin="10" Tapped="Add_Apple" VerticalAlignment="Center"/&gt;
      &lt;StackPanel x:Name="TotalStackPanel" Margin="10" Orientation="Vertical" HorizontalAlignment="Center"&gt;
          &lt;TextBlock Text="Total" Margin="10" HorizontalAlignment="Center"/&gt;
          &lt;GridView x:Name="TotalFruitGrid" SelectionChanged="Remove_Fruit"&gt;
              &lt;GridView.ItemTemplate&gt;
                  &lt;DataTemplate&gt;
                      &lt;Image Source="{Binding Path=image.Source}" Height="50"/&gt;
                  &lt;/DataTemplate&gt;
              &lt;/GridView.ItemTemplate&gt;
          &lt;/GridView&gt;
      &lt;/StackPanel&gt;
      &lt;Image Width="100" x:Name="OrangeImage" Source="/Assets/Images/orange.png" Margin="10" Tapped="Add_Orange" VerticalAlignment="Bottom"/&gt;
  &lt;/RelativePanel&gt;
  </code></pre>