title: xceed DataGridControl custom type filtering doesn't work
body: <p>I have a problem with the <code>FilterRow</code> of a <code>Xceed DataGridControl</code>.</p>
  
  <p>In my <code>DataGridControl</code> I have a column in which a custom <code>type(Car)</code> is the content.
  I have added a <code>FilterRow</code> to the <code>DataGrid</code> and there is a <code>FilterCell</code> displayed for every Column except for the Column with the custom <code>type(Car)</code>.
  I managed to get the custom types property <code>(Car.Name)</code> to be shown in the Column but I still can't filter over it.</p>
  
  <p>Here is my XAML:</p>
  
  <pre><code>&lt;!--Car-Column--&gt;
      &lt;xcdg:Column Title="Car" FieldName="Car"&gt;
        &lt;xcdg:Column.CellEditor&gt;
          &lt;xcdg:CellEditor&gt;
            &lt;xcdg:CellEditor.EditTemplate&gt;
              &lt;DataTemplate&gt;
                &lt;ComboBox 
                  ItemsSource="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType= UserControl}, Mode=OneWay, Path=DataContext.AvailableCarList}"
                  DisplayMemberPath="Name"
                  SelectedValue="{xcdg:CellEditorBinding}"&gt;
                &lt;/ComboBox&gt;
              &lt;/DataTemplate&gt;
            &lt;/xcdg:CellEditor.EditTemplate&gt;
          &lt;/xcdg:CellEditor&gt;
        &lt;/xcdg:Column.CellEditor&gt;
        &lt;xcdg:Column.CellContentTemplate&gt;
          &lt;DataTemplate&gt;
            &lt;TextBlock Text="{Binding Name, Mode=OneWay}"/&gt;
          &lt;/DataTemplate&gt;
        &lt;/xcdg:Column.CellContentTemplate&gt;
      &lt;/xcdg:Column&gt;
  </code></pre>
  
  <p>I also read the Documentation of the <code>Xceed DataGridControl</code> and followed their order to implement the IComperable Interface for Car and also added a TypeConverter, but it still didn't work for me.</p>