title: Gwt "Double" cell-widget number formatting
body: <p>I have this in my uiBinder:</p>
  
  <p>
                          
                              
                          
                      </p>
  
  <p>Declared as @UiField ValueBoxEditorDecorator importoEditor; in my code.</p>
  
  <p>It behaves correctly: "50" displays as "50.0".
  Now I want to display it as "50.00", since it is a currency euro value.</p>
  
  <p>How can I set a number formatter on that field?</p>