title: how to add a custom entry in UIActivityViewController
body: <p>When i open an attachment from iPhone or iPad mail application, there is a popup that can transfert the file to a third party application.</p>
  
  <p>This iOS popup is called UIActivityViewController.</p>
  
  <p>I wand to add my own iOS application (written in swift) in this popup and i do not know how to do...</p>
  
  <p>Thanks</p>