Allow to enable/disable bNode support for the SesameYard

Currently the SesameYard recursively includes also Statements having BNodes as subjects that are referenced as Object by the extracted Representation. While those information are not accessible via the Entityhub API they are stored in the Sesame Model (and therefore e.g. accessible to Sesame Serializers).

Adding this option will allow to disable this feature for a SesameYard