Model Update and PBR object updating

This release improves consistency between local and remote objects. After an object is saved, any fields that are set in the remote object and not local one (GUID, UpdatedDate etc.) are populated in the local object.

This also enables you to determine which objects were successfully saved from a batch, as one failed item will not disrupt the whole batch. For new objects, the easiest way to confirm that it was successful is to check the ->hasGUID() method after saving.

Further discussion on enhancement #12