Add GZip compression support to Fuseki

The attached patch for Fuseki gives the user the ability to enable gzip compression either by using a --gzip option at the command line or by calling ARQ.set(Fuseki.FusekiEnableGZipCompression, true) from code

GZip compression is enabled by adding the GzipFilter to relevant servlets, this filter comes from the jetty-servlets package which is licensed under the same terms as the existing Jetty dependencies used so I assume licensing is not an issue. When enabled GZip compression only applies when the client sends an Accept-Encoding: gzip header and certain other conditions are met.

Currently this feature is disabled by default as most browsers will send this header and when both the client and server are on the local machine performance can actually be worsened. When the client and server are on different networks a significant speed up (2-5x times depending on result format) has been seen.