message: improve selected and mouseover DataGrid row coloring
diff: <Setter Property="mah:ControlsHelper.ContentCharacterCasing" Value="Normal"/>
  </Style>
  - <SolidColorBrush x:Key="MahApps.Brushes.DataGrid.Selection.Background" Color="{DynamicResource MahApps.Colors.Accent4}" />
  - <SolidColorBrush x:Key="MahApps.Brushes.DataGrid.Selection.Background.Inactive" Color="{DynamicResource MahApps.Colors.Accent4}" />
  + <SolidColorBrush x:Key="MahApps.Brushes.DataGrid.Selection.Background" Color="Transparent" />
  + <SolidColorBrush x:Key="MahApps.Brushes.DataGrid.Selection.Background.Inactive" Color="Transparent" />
  + <SolidColorBrush x:Key="MahApps.Brushes.DataGrid.Selection.Background.MouseOver" Color="{DynamicResource MahApps.Colors.Accent4}" />
  </UserControl.Resources>
  <i:Interaction.Triggers>
  <i:EventTrigger EventName="Loaded">
  