Add a InteractiveDialog demo for the DialogExtension.

HandyControlDemo/UserControl/Basic/InteractiveDialog.xaml.cs

@@ -0,0 +1,13 @@
+namespace HandyControlDemo.UserControl.Basic
+{
+    /// <summary>
+    /// Interaction logic for InteractiveDialog.xaml
+    /// </summary>
+    public partial class InteractiveDialog
+    {
+        public InteractiveDialog()
+        {
+            InitializeComponent();
+        }
+    }
+}