Fix up site preview images

Updates the site preview images to match the latest design, updates the favicon and removes a bunch of the OS-specific icons.

Author: crisbeto

scenes/src/app/scene-viewer/scene-viewer.scss

@@ -13,4 +13,5 @@ app-scene-viewer {
   top: 0;
   height: 100%;
   width: 100%;
+  pointer-events: none;
 }