title: flutter implement sticky headers and the snap to item effect
body: <p>For the last few days, I've been reading through flutter framework documentation and especially the sliver part but I'm not quite sure where to start.
  I'm trying to implement the sticky headers and snap effect.
  Might the RenderSliverList be a good start? Do I need to re-layout things? Do I need to do additional drawing? And if so where?</p>
  
  <p>Any help on where to start would be a huge help, thanks in advance!</p>
  
  <p>Edit: I think I understood the layout part now, but I just can't find where the painting is supposed to happen.</p>
  
  <p>Edit 2: For clarification, this is the desired "sticky header effect": </p>
  
  <p><a href="https://stackoverflow.com/questions/32949971/how-can-i-make-sticky-headers-in-recyclerview-without-external-lib">How can I make sticky headers in RecyclerView? (Without external lib)</a></p>
  
  <p>and this is the "snap" effect:</p>
  
  <p><a href="https://rubensousa.github.io/2016/08/recyclerviewsnap" rel="noreferrer">https://rubensousa.github.io/2016/08/recyclerviewsnap</a></p>