Add HTTP content negotiation for the IIIF info request

[robcast]

A client should be able to specify the preferred IIIF protocol version using content-negotiation: https://iiif.io/api/image/3.0/#51-image-information-request

Implementation should likely go in digilib.servlet.ServletOps.sendIiifInfo(DigilibServletRequest, HttpServletResponse, Logger)