title: add item to next column in wrapgrid
body: <p>I have a <code>GridView</code> like this</p>
  
  <pre><code>&lt;GridView x:Name="TestGridView"  SelectionMode="None"&gt;                
    &lt;GridView.ItemsPanel&gt;
      &lt;ItemsPanelTemplate&gt;
        &lt;WrapGrid Orientation="Vertical" ItemWidth="300" ItemHeight="80"  Height="480" VerticalAlignment="Top"  /&gt;
      &lt;/ItemsPanelTemplate&gt;
    &lt;/GridView.ItemsPanel&gt;
  &lt;/GridView&gt;
  </code></pre>
  
  <p>One of my <code>GridViewItem</code> contains a button, when I click this <code>Button</code>, a new <code>GridViewItem</code> will added to the <code>GridView</code> dynamically, I want the maximum number of <code>GridViewItem</code> is 8, after the eighth <code>GridViewItem</code> added to the <code>GridView</code>, the <code>Button</code> collapsed. Then add some other <code>GridViewItem</code> in next column of the <code>GridView</code>, but the 8th <code>GridViewItem</code> doesn't occupy all the space of the 2nd column, if I add new <code>GridViewItem</code>, it will automatically added to the 2nd column below the 8th <code>GridViewItem</code>. How to explicitly add <code>GridViewItem</code> to the next column?</p>