title: When an Activator class/"Bundle-Activator" is needed in plug-in and when it's not?
body: <p>I've implemented "New Wizard" plug-in for my content-type.
  Tested it - it works.</p>
  
  <p>Then I've found that neither Bundle-Activator was declared, nor the Activator class was defined.</p>
  
  <p>The question is - when the Activator class is really needed in plug-in.
  And when it doesn't needed at all?</p>