title: Add a scroll to top button (Ionic 2 | Typescript)
body: <p>Hi everyone i am trying to add "scroll to top button." that implement the following :</p>
  
  <p>1.Show the button when user has scrolled down.
  2.Hide the button when the user scrolls up.
  3.If the button is tapped then scroll to the top and hide the button .
  any suggestion for how make it right way?</p>
  
  <p>thanks a lot </p>