title: How to start a file download in vaadin without button?
body: <p>I know that it is really easy to create a <code>FileDownloader</code> and call extend with a <code>Button</code>. But how do I start a download without the <code>Button</code>? <br>
  In my specific situation right now I have a <code>ComboBox</code> and the file I'd like to send to the user is generated after changing its value, based on the input. The file should be sent immediately without waiting for another click. Is that easily possible?</p>
  
  <p>Thanks
  raffael</p>