improve growl

According to @ghost1372  suggestion, growl has been improved.

DockBoxResearch/Controls/DocDockBoxItemPanel.cs

@@ -0,0 +1,9 @@
+using System.Windows.Controls;
+
+namespace DockBoxResearch.Controls
+{
+    public class DocDockBoxItemPanel : Panel
+    {
+        
+    }
+}