Allow to optionally pass `namespace` to ClosedOntologyNamespace, DefinedOntologyNamespace

[lu-pl]

ClosedOntologyNamespace and DefinedOntologyNamespace try to read the ontology namespace from the ontology header. If this fails, Namespace instantiation fails.

Those classes could provide an optional parameter namespace to explicitly set an ontology namespace; if namespace is provided, the classes will not try to infer the namespace from the ontology and will check attribute access for classes and properties of that namespace.