title: Add listener to SpanElement
body: <p>I wanna add mouse over listener to SpanElement, which i created by:</p>
  
  <pre><code>SpanElement span = Document.get().createSpanElement();
  span.setInnerText("my text");
  </code></pre>
  
  <p>I found in google how to do it with Label-wrapper, but I wanna to do it without any wrappers. Is it possible?</p>
  
  <p>Thank you.</p>