[New feature] when an IIIF image download fail, display the URL of the full image to the user

[lovasoa]

Sometimes the info.json is not available, but you can still download the full image from the server using the IIIF server's own capabilities:

https://github.com/lovasoa/dezoomify/wiki/How-to-download-full-resolution-images-from-an-IIIF-compatible-server

We could have a message that shows, "try this URL".

This would help in cases like this: https://github.com/lovasoa/dezoomify/issues/522