title: Expand first group and collapse remaining group by default using zk
body: <p>I have created a MyGroupModelList class by extending the AbstractGroupsModel class. I want first group present in MyGroupModelList should be expanded and remaining all other groups should be collapsed.</p>
  
  <p>On the viewModel I have written Below.</p>
  
  <pre><code>private MyGroupModelList &lt;TabData&gt; summaryGroupModel;
  
  @AfterCompose
  public void afterCompose(@ContextParam(ContextType.VIEW) Component view){    
  summaryGroupModel = getSummaryTabData(folderRSN);
  
  if (summaryGroupModel != null &amp;&amp; summaryGroupModel.getGroupCount() &gt; 0) {
  summaryGroupModel.addOpenGroup(0);
  }
  </code></pre>
  
  <p>On the ZUL have written Below.</p>
  
  <pre><code>&lt;zk&gt;
  
   &lt;window width="100%" height="100%"
      apply="org.zkoss.bind.BindComposer"
      viewModel="@id('vm') @init('com.test.MyGroupModelList ')"&gt;
  
  
      &lt;listbox model="@bind(vm.summaryGroupModel.groupModel)"&gt;
  
          &lt;listhead&gt;
              &lt;listheader label="Bill Number"&gt;&lt;/listheader&gt;
              &lt;listheader label="Bill Amount"&gt;&lt;/listheader&gt;
  
          &lt;/listhead&gt;
  
          &lt;template name="model" var="Data"&gt;
              &lt;listitem&gt;
                  &lt;listcell&gt;
                      &lt;label value="@load(Data.billNumber)" /&gt;
                  &lt;/listcell&gt;
                  &lt;listcell&gt;
                      &lt;label value="@load(Data.billAmount)" /&gt;
                  &lt;/listcell&gt;
  
              &lt;/listitem&gt;
          &lt;/template&gt;
      &lt;/listbox&gt;
  &lt;/window&gt;
  &lt;/zk&gt;
  </code></pre>
  
  <p>Above code is not expanding first group present in MyGroupModelList.</p>
  
  <p>Please help</p>