Work on low-level ObjectModelSelectKey and ...

... associated ObjectStoreNamespaceKeyResolver classes. ObjectModelSelectKey encapsulates an entension point, key, namespace tuple. ObjectStoreNamespaceKeyResolver is used to resolve an actual store namespace given an ObjectModelSelectKey instance. Vectors of ObjectModelSelectKey objects are to be the basis of the new OMM ObjectModelSelector. Similarly, vectors of ObjectStoreNamespaceKeyResolver instances are to underpin ObjectStoreNamespace.