Remove dependency on Zoom.it combo viewer; use Seadragon Ajax instead

[Aseem Kishore]

Right now, Zoom.it Lightbox uses the undocumented hosted Zoom.it combo viewer. This was initially done because it was my hope that we could publicly release this Lightbox officially hosted on Zoom.it. With the disbanding of Live Labs, though, that's not going to happen. And worse, the combo viewer is now stagnant; it's not possible for us to fix bugs or improve it as needed.

So we should switch the viewer to use Seadragon Ajax instead, which is both public and official and allows us to continue improving the viewing experience as needed. Two things we're going to miss from the Zoom.it combo viewer, though, are the Silverlight support and the Zoom.it branding. See these two work items to add these features into Seadragon Ajax:

• Silverlight support
• Branding support