For developers: Create a class for the custom widget
 The backbone of the designer is a custom widget. It allows you to wrap existing designer views into a multi-view designer. The custom widget can reside either in the project of the targeted widget or in a separate project. Because the designers are usually coupled with a specific widget, we recommended creating the designer in the same project as the widget. 
 To create the class for the designer, perform the following.
  - Add a new class to the project of the targeted widget.
 For example, if your widget is named Rotator, create a class named RotatorDesigner.
 Perform the following:  - In the context menu of References, click Add Reference...
  - Click Browse tab and navigate to folder C:\Program Files (x86)\Telerik\Sitefinity CMS 4.0\Libraries.
  - Select the assembly and click OK.
  
   - Add a reference to the System.Web.Extensions assembly.
 Perform the following  - In the context menu of References, click Add Reference...
  - Click the .NET tab, select the assembly, and click OK.
  
   - Add statement using Telerik.Sitefinity.Web.UI.ControlDesign; to the RotatorDesigner class.
  - Make the RotatorDesigner class inherit the ContentViewDesignerBase class in the following way:
   public class RotatorDesigner : ContentViewDesignerBase
 {
 }