title: Ext Gwt checkbox listener
body: <p>I am using Ext GWT. I have created a Grid with a CheckColumnConfig with a CheckBox inside it. I want to put a listener on the checkbox in order to allow single selection on the grid. The problem is that no listener seems working. I am using the method addListener trying with the event Events.Change Events.Changed and Events.OnClick but it seems they are not working properly. How can I attach a listener on check change?</p>
  
  <p>Thanks</p>