message: indent child items in TreeView
diff: <ColumnDefinition Width="{Binding ElementName=tblSizeColHdr, Path=ActualWidth}" />
  <ColumnDefinition Width="{Binding ElementName=tblDbPctColHdr, Path=ActualWidth}" />
  </Grid.ColumnDefinitions>
  - <controls:WarningWithTooltip Margin="-32,9,0,0" Visibility="{Binding IsRequired, Converter={StaticResource BooleanToVisibilityConverter}}" />
  - <CheckBox Margin="-12,0,0,0" IsChecked="{Binding IsSelected, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Style="{StaticResource MahApps.Styles.CheckBox.Win10}" />
  - <TextBlock Margin="-10,0,0,0" Text="{Binding ColumnName, Mode=OneWay}" VerticalAlignment="Center" Grid.Column="1"/>
  + <controls:WarningWithTooltip Margin="-10,9,0,0" Visibility="{Binding IsRequired, Converter={StaticResource BooleanToVisibilityConverter}}" />
  + <CheckBox Margin="12,0,-6,0" IsChecked="{Binding IsSelected, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Style="{StaticResource MahApps.Styles.CheckBox.Win10}" />
  + <TextBlock Margin="12,0,0,0" Text="{Binding ColumnName, Mode=OneWay}" VerticalAlignment="Center" Grid.Column="1"/>
  <TextBlock Margin="-10,0,15,0"
  Text="{Binding Cardinality, Mode=OneWay, Converter={valueconverters:SimplifyNumberConverter}}"
  HorizontalAlignment="Right"
  