LinkedGeoData conformance to final GeoSPARQL spec

See also https://github.com/AKSW/Sparqlify/issues/20

One thing I didn't really look at and that might need to be changed, is the namespace for functions like in [FunctionExpander] (https://github.com/brunksn/Sparqlify/blob/1f1203c5525147c23b9ed32048114c8010b087c4/sparqlify-core/src/main/java/org/aksw/sparqlify/algebra/sparql/transform/FunctionExpander.java)