title: Add row as group header in datagrid
body: <p>I am using wpf toolkit's datagrid i want to marge a row for all its columns when a property IsGroup is set as true. i want to use datatrigger insteed of ivalueconverter. i have done it with ivalueconverter. 
  One more thing is that i dont want to use the grouping functionality of datagrid. just want ted to add row at specific index no and make that row as single column. so will look like group name </p>
  
  <pre><code>&lt;my:DataGrid.RowStyle&gt;
                  &lt;Style TargetType="{x:Type my:DataGridRow}"&gt;
                      &lt;Setter Property="Background" Value="White" /&gt;                      
                      &lt;Setter Property="Background" Value="{Binding IsGroup, Converter={StaticResource rowhighlighter}}" /&gt;
                      &lt;!--&lt;Style.Triggers&gt;
                          &lt;DataTrigger Binding="{Binding IsGroup,UpdateSourceTrigger=PropertyChanged}" Value="True"&gt;
                              &lt;Setter Property="Background" Value="YellowGreen"/&gt;
                          &lt;/DataTrigger&gt;
                      &lt;/Style.Triggers&gt;--&gt;
                  &lt;/Style&gt;
              &lt;/my:DataGrid.RowStyle&gt;
  </code></pre>
  
  <p>this style datatrigger is not working for me where i am wrong. </p>