message: Hide descriptionLabel when there is no description (win)
diff: <TextBlock Grid.Row="0" Name="descriptionLabel" x:FieldModifier="private"
  MouseLeftButtonDown="onDescriptionLabelMouseDown"
  Style="{StaticResource Toggl.BodyText}"
  + Visibility="{Binding Description, Converter={StaticResource EmptyStringToCollapsedConverter}}"
  Text="{Binding Description}"
  ToolTip="{Binding Description}">
  </TextBlock>
  