upgraded growl

now if user do not set hc:Growl.GrowlParent="True", growl will create a default panel.

src/Shared/HandyControlDemo_Shared/UserControl/Main/MainWindowContent.xaml

@@ -1,5 +1,4 @@
 <Border xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
-        xmlns:hc="https://handyorg.github.io/handycontrol"
         BorderThickness="0,1,0,0" 
         BorderBrush="{DynamicResource BorderBrush}" 
         Background="{StaticResource CloudDrawingBrush}"
@@ -14,8 +13,5 @@
         <userControl:LeftMainContent/>
         <userControl:MainContent Grid.Column="1"/>
         <GridSplitter Margin="0,26,0,26" Grid.Column="0" HorizontalAlignment="Right" Width="4" Background="Transparent"/>
-        <hc:ScrollViewer Grid.Column="1" VerticalScrollBarVisibility="Hidden" HorizontalAlignment="Right" IsInertiaEnabled="True" IsPenetrating="True">
-            <StackPanel hc:Growl.GrowlParent="True" VerticalAlignment="Top" Margin="0,10,10,10"/>
-        </hc:ScrollViewer>
     </Grid>
-</Border>
+</Border>