title: "Book like" view in Openseadragon (several "2 pages" sequences)
body: <p>Openseadragon newbbie here !</p>
  
  <p>I'm trying to display images by group of 2 AND keeping sequence mode activated, so I can "turn pages".</p>
  
  <p>I managed to display 2 pages, I managed to read pages 1 by 1 in sequence mode, ... 
  But I just didn't find a way to do both.</p>
  
  <p>To display 2 pages, I loaded 2 tiles sets and configured "sequenceMode=false". Then I set coordinates, to display visuals aside.</p>
  
  <p>To read pages 1 by 1, I loaded several tiles and configured "sequenceMode = true".</p>
  
  <p>What I would like to do is display two visuals (= tiles sets) aside (like an open book). And then, on "next" button click, display the two next visuals from my "tilesSources" array... and so on !</p>
  
  <p>Thank you for your help !</p>