move fog:referencedContent to OMG

[mathib]

I think fog:ReferencedContent and fog:hasReferencedContent should move from FOG to OMG, as it can be applicable to more then one geometry schema.

The above terminology is now used when connecting a building object to an RDF literal with embedded geometry description and the content and name of an additional file also has to be connected (e.g. a material file in the case of OBJ, or a texture file in the case of OBJ/glTF or an additional binary geometry file in glTF):

inst:door1 omg:hasGeometry inst:geometry1 .
inst:geometry1 a omg:Geometry ;
   fog:asObj_v3.0-obj "v 1 0 2 ..."^^xsd:string ;
   fog:hasReferencedContent inst:ref1 .
inst:ref1 a fog:ReferencedContent ;
   fog:asObj_v3.0-mtl "newmtl Mat_1\n Ka 0.000 ..."^^xsd:string ;
   rdfs:label "mymtlfile.mtl" .

[AnnaWagner]

Add a new node to OMG for geometry textures/materials - Node should be able to describe both. Specific subclasses/properties should be part of FOG, then.
Approach-independent