IIIF Image API 1.1 Tile Source

Adds support for the [IIIF 1.1 Image Information syntax](http://www-sul.stanford.edu/iiif/image-api/1.1/#info). Most Notably:

 * The XML syntax is gone. :boom: 
 * The JSON syntax is now json-ld, which means the [hack for adding a tilesUrl](https://github.com/openseadragon/openseadragon/blob/master/src/iiiftilesource.js#L135) is no longer necessary because `info['@id']` can be used.
 * The size argument is now pixel-based (1.0 is percent based), which leads to more efficient caching on the server.

See it in action here: http://libimages.princeton.edu/osd-demo

Please keep the IIIF Tile Source around, at least for a while, as others are likely still using it.

Also I would prefer if the opensedragon.github.io site would point to the above server. Once this request is merged, I'd be happy to update that site's repo if you'd like.