title: How to get all notification of all application have custom notification running
body: <p>I'm a beginner. I have a problem about custom notification.
  I want to read all information of normal notification and custom notification use RemoteView.
  Example I want get all information about notification music(art cover, song, next, pause, back action)
  I search very very much, but can't find the document I need.
  If you know, please tell me.
  Thank so much!</p>