Move Fuseki integration to a Jena module

[Ostrzyciel]

Follow-up from #136

Fuseki modules are not supported in all Fuseki distributions, so it makes more sense to move the functionality to a Jena module. The only disadvantage is that the module loads regardless of whether we are in a Fuseki instance or not, but that can be solved with some exception catching...

I tested this on:

• Fuseki 5.2.0: works perfectly and displays a message that the media type was registered
• Fuseki 5.1.0: displays a warning that the registration doesn't work because Fuseki is too old
• Jena CLI utils: module initialization fails silently, the CLI tool works as expected