title: How to align buttons to the center in horizontal panel?
body: <p>I have a horizontal panel and 2, sometimes 3 buttons.</p>
  
  <pre><code>Button btn1 = new Button("Ok");
  Button btn2 = new Button("Cancel");
  HorizontalPanel panel = new HorizontalPanel();
  panel.setWidth(100%);
  panel.add(btn1);
  panel.add(btn2);
  panel.setHorizontalAlignment(HasHorizontalAlignment.ALIGN_CENTER);
  </code></pre>
  
  <p>But only cancel button is in the center then. But how to align both...or even any number of buttons to the center on one horizontal panel?</p>