title: Multiple select list with actionListeners?
body: <p>I want to achieve the following:</p>
  
  <ul>
  <li><p>It should be possible to create entries, and these entries (Strings) should be displayed as a list. A list entry should be selectable (with listener method on each entry) by a single click, without holding any keyboard buttons. Also clicking an already selected entry should deselect it.</p></li>
  <li><p>Also, an entry should get a dimension, which will specify the number of subentries. These should be visible by some kind of expand button before the entry. Again, subentries should also be multiple selectable.</p></li>
  </ul>
  
  <p>Are there components that already provide such a feature? If not, what should I look into to build such a component?</p>