title: eclipse e4 PartStack change listener
body: <p>i need a listener for my partstack when someone clicks on another tab.</p>
  
  <p>I have seen that PartStack should have an function addListener. But it seems this function is not avaliable anymore :(</p>
  
  <p><a href="https://www.cct.lsu.edu/~rguidry/ecl31docs/api/org/eclipse/ui/internal/PartStack.html" rel="nofollow">https://www.cct.lsu.edu/~rguidry/ecl31docs/api/org/eclipse/ui/internal/PartStack.html</a></p>
  
  <p>Also the idea to register an IPartListener on EPartService seems to be wrong here.</p>