sub schema (SchemaAttributePathInstance) domain model extension + test re-factoring

* incl. new init_internal_schema.sql script (+ generation via code)
this is still the old schema building code. there should be something newer in my fork, we may want to merge soon. This shouldn't cause errors, but I think the front end does not yet need to be able to handle both - flat structures with long attribute paths AND the subschema-approach. Longer paths as given here could only be interpreted to create a node of type rdfs:Resource, since no other type information is given.