add a notifications page to control catalog

samples/ControlCatalog/MainView.xaml

@@ -29,6 +29,8 @@
       <TabItem Header="LayoutTransformControl"><pages:LayoutTransformControlPage/></TabItem>
       <TabItem Header="ListBox"><pages:ListBoxPage/></TabItem>
       <TabItem Header="Menu"><pages:MenuPage/></TabItem>
+      <TabItem Header="Notifications"><pages:NotificationPage/></TabItem>
+	  <TabItem Header="NumericUpDown"><pages:NumericUpDownPage/></TabItem>
 	  <TabItem Header="NumericUpDown"><pages:NumericUpDownPage/></TabItem>
       <TabItem Header="ProgressBar"><pages:ProgressBarPage/></TabItem>
       <TabItem Header="RadioButton"><pages:RadioButtonPage/></TabItem>

samples/ControlCatalog/Pages/NotificationsPage.xaml

@@ -0,0 +1,9 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             x:Class="ControlCatalog.Pages.NotificationsPage">
+  <StackPanel Orientation="Vertical" Spacing="4">
+        <Button Content="Show Custom Managed Notification" />
+        <Button Content="Show Standard Managed Notification" />
+        <Button Content="Show Native Notification" />
+    </StackPanel>
+</UserControl>

samples/ControlCatalog/Pages/NotificationsPage.xaml.cs

@@ -0,0 +1,18 @@
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace ControlCatalog.Pages
+{
+    public class NotificationsPage : UserControl
+    {
+        public NotificationsPage()
+        {
+            this.InitializeComponent();
+        }
+
+        private void InitializeComponent()
+        {
+            AvaloniaXamlLoader.Load(this);
+        }
+    }
+}