Creates a new Cogxel for the given CogxelFactory from the given
SemanticIdentifier. If this factory can create a Cogxel from the given
SemanticLabel, then a new Cogxel with that label is created. If the
factory cannot create a Cogxel for the given SemanticIdentifier, then
null is returned.
identifier - The SemanticIdentifier of the new Cogxel
A new Cogxel for the given model from the given identifier, if
the factory can create a Cogxel from the given identifier. If
it cannot, null is returned.