title: DataGrid's CellEditingTemplate and focus in edit mode
body: <p>I am having an issue with WPFToolkit <code>DataGrid</code> when a column is customized supplying both <code>CellTemplate</code> and <code>CellEditingTemplate</code>. If you take a look below, you will see my editing template has a single <code>CheckBox</code>. All is fine in a functional sense but when F2 is hit to edit the cell, one must also hit TAB in order for the <code>CheckBox</code> to receive focus. Ideally, one would hit F2 and SPACE to toggle the value. Currently, one must hit F2, TAB, SPACE. I have tried setting <code>TabIndex</code> to no avail. I am running out of ideas.</p>
  
  <pre><code>&lt;WPFToolkit:DataGridTemplateColumn Header="Turn"
                                     MinWidth="60"&gt;
      &lt;WPFToolkit:DataGridTemplateColumn.CellTemplate&gt;
          &lt;DataTemplate&gt;
              &lt;Image Height="16"&gt;
                  &lt;Image.Style&gt;
                      &lt;Style TargetType="{x:Type Image}"&gt;
                          &lt;Style.Triggers&gt;
                              &lt;DataTrigger Binding="{Binding CanTurn}" Value="True"&gt;
                                  &lt;Setter Property="Source" Value="/Images/16/Tick.png" /&gt;
                              &lt;/DataTrigger&gt;
                          &lt;/Style.Triggers&gt;
                      &lt;/Style&gt;
                  &lt;/Image.Style&gt;
              &lt;/Image&gt;
          &lt;/DataTemplate&gt;
      &lt;/WPFToolkit:DataGridTemplateColumn.CellTemplate&gt;
  
      &lt;WPFToolkit:DataGridTemplateColumn.CellEditingTemplate&gt;
          &lt;DataTemplate&gt;
              &lt;CheckBox IsChecked="{Binding Path=CanTurn}" HorizontalAlignment="Center" HorizontalContentAlignment="Center" /&gt;
          &lt;/DataTemplate&gt;
      &lt;/WPFToolkit:DataGridTemplateColumn.CellEditingTemplate&gt;
  &lt;/WPFToolkit:DataGridTemplateColumn&gt;
  </code></pre>