examples/deepzoom: Avoid loading smallest Deep Zoom levels

in deepzoom_server and deepzoom_tile.  The smallest levels are a waste
of network round trips.

Author: bgilbert

examples/deepzoom/templates/slide-multipane.html

@@ -124,6 +124,13 @@ <h1>Slide properties</h1>
         visibilityRatio: 1,
         zoomPerScroll: 2,
     });
+    viewer.addHandler("open", function() {
+        // To improve load times, ignore the lowest-resolution Deep Zoom
+        // levels.  This is a hack: we can't configure the minLevel via
+        // OpenSeadragon configuration options when the viewer is created
+        // from DZI XML.
+        viewer.source.minLevel = 8;
+    });
 
     function open_slide(url) {
         var tile_source;