As reported by @reger24, image and favicon viewing was broken with
unauthenticated requests on peers configured to require authentication
even from localhost.
So I unified viewing rights check in a single new function on
ImageViewer class.
to make all readily available information from the original ServletRequest
available to YaCy servlets (without converting data to internal structures).
The implementation of the common interface allows easier integration of
YaCy servlets with the servlet standard (e.g. shared login service with
the servlet container etc.)
Main image processing is now in ImageViewer, used by both ViewImage and
ViewFavicon.
Fixed URIMetadataNode.getFavicon to use non-standard icons with no size
ass fallback.