title: Checkbox column for multiple rows when shift keyboard modifier is applied
body: <p>I have a view model that contains an "IsChecked" property.  This property is bound to a DataGrid RowHeaderTemplate. </p>
  
  <p>I'd like to be able to hold down the shift + ctrl keyboard modifiers to allow for multiple checkbox values to be updated.  </p>
  
  <p>For example: If you check the checkbox in the first row, hold down shift, and check the checkbox in the 5th row; rows 1-5 would then have a checked checkbox.</p>
  
  <p>Below is the row header template:</p>
  
  <pre><code>&lt;DataGrid.RowHeaderTemplate&gt;
      &lt;DataTemplate&gt;
          &lt;CheckBox VerticalAlignment="Center"
                    VerticalContentAlignment="Center"
                    IsChecked="{Binding IsChecked}" /&gt;
      &lt;/DataTemplate&gt;
  &lt;/DataGrid.RowHeaderTemplate&gt;
  </code></pre>
  
  <p>I've tried several combinations of capturing PreviewMouseLeftButtonDown and KeyPress events, but I'm not sure this is even possible with a bound property.</p>