title: UI get value function not work in Document App
body: <p>looks like the e.parameter.name method to get text box value is not worked on document UI,
  For example, in main UI </p>
  
  <p>=============================================================</p>
  
  <pre><code>var app = UiApp.createApplication().setWidth(455).setTitle('My UiApp Sidebar');
  var panel = app.createVerticalPanel()
  var textBoxA =   app.createTextBox()
                      .setId('textBoxA')
                      .setName('textBoxA').setTag('textBoxA');
  
  
  var clickButton=app.createButton("Paste")
                     .setId("PasteTest")
                     .addClickHandler(pasteHandler) 
  
  
  var pasteHandler = app.createServerChangeHandler('readTextbox');
  pasteHandler.addCallbackElement(panel);
  
  panel.add(textBoxA);
  panel.add(clickButtion);
  app.add(panel);
  DocumentApp.getUi().showSidebar(app);
  </code></pre>
  
  <p>======================================================================</p>
  
  <p>then in event handler</p>
  
  <pre><code>readTextbox(e){
    var app = UiApp.getActiveApplication(); 
  var boxValue=e.parameter.textBoxA;
    return app;
  }
  </code></pre>
  
  <p>the boxValue return undifined, the e.parameter.textBoxA_Tag also not work, i put the e.paramter in log, not textBoxA in there.</p>
  
  <p>It is works fine in Spreadsheet UI, looks like not support document UI very well</p>