title: adding text to a combobox with a datasource
body: <p>I have a vaadin combobox that is filled with a containerdatasource</p>
  
  <pre><code>setContainerDataSource(container);
  </code></pre>
  
  <p>I now want to insert a static text somewhere in the list of results.</p>
  
  <hr>
  
  <p>For example:</p>
  
  <p>A Combobox that is filled with a container of  and the first entry that pops up in the result list is some kind of header:</p>
  
  <p>Persons:<br>
  Thomas S.<br>
  Lucas B.<br>
  Alex X.</p>
  
  <p>Can i achieve that by either manipulating the container or the combobox?</p>
  
  <p>I just tried to set the container source and add a String/Label via addItem() to the ComboBox, but that doesn't seem to work. I am kinda new to this, so I don't know how to continue.</p>