Moved all PInvokes to a lower class without any relianceon WPF, NotificationIconHelper, TaskbarHelper, SystemPersonalisationHelper are WPF window no more

src/NotificationFlyout.Shared.UI/INotificationFlyoutApplication.cs

@@ -0,0 +1,11 @@
+using Windows.UI.Xaml;
+
+namespace NotificationFlyout.Uwp.UI
+{
+    public interface INotificationFlyoutApplication
+    {
+        void Exit();
+
+        void OpenAsWindow<TUIElement>() where TUIElement : UIElement;
+    }
+}