GroupStyle changed

                       <DataTemplate>
                            <Grid Margin="1,0,0,6">
                                <Button Foreground="{StaticResource ApplicationHeaderForegroundThemeBrush}"
                                    AutomationProperties.Name="Group Title"
                                    Click="Header_Click"
                                    Style="{StaticResource TextBlockButtonStyle}" >
                                    <Grid>
                                        <Grid.RowDefinitions>
                                            <RowDefinition />
                                            <RowDefinition />
                                        </Grid.RowDefinitions>
                                        <StackPanel Orientation="Horizontal">
                                            <TextBlock Text="{Binding Title}" Margin="3,-7,10,10" Style="{StaticResource HeaderTextBlockStyle}" TextWrapping="NoWrap" />
                                            <TextBlock Text="{StaticResource ChevronGlyph}" FontFamily="Segoe UI Symbol" Margin="0,-7,0,10" Style="{StaticResource SubheaderTextBlockStyle}" TextWrapping="NoWrap" />
                                        </StackPanel>
                                        <TextBlock Grid.Row="1" Text="{Binding Subtitle}" Margin="3,-7,10,10" Style="{StaticResource SubheaderTextBlockStyle}" TextWrapping="NoWrap" />
                                    </Grid>
                                </Button>
                            </Grid>
                        </DataTemplate>