Add local extraction cache to Any23 service

It would be nice to have a caching mechanism for the Any23 service which resides at any23.org (and for the service module generally).
This cache would consist of a HashMap which would essentially index extraction results based on HashMap<URL, TriplesStream>. Right now I am pretty sure that TriplesStream will be something like ExtractionResultImpl, however I still have to find this out once I look further into the concrete implementation.