message: Add gray line below the day header (win)
diff: </Grid.RowDefinitions>
  <StackPanel Grid.Row="1" Name="panel" x:FieldModifier="private"
  Visibility="{Binding IsExpanded, Converter={StaticResource BooleanToVisibilityConverter}}"
  - Margin="0 -1 0 0"
  Background="{DynamicResource Toggl.LightGrayBrush}"/>
  <!-- <ItemsControl Visibility="{Binding IsExpanded, Converter={StaticResource BooleanToVisibilityConverter}}" -->
  <!-- Items="{Binding DaysBindable}" /> -->
  