Working on #2: helper method for sending event notifications through nodes
Working on #2: more observer debugging support
Working on #2: remove literal properties
Working on #2: remove properties with resource refs and blank node refs
Working on #2: assert event parameters too
Working on #2: remove blank node properties
Working on #2: improve logging of model objects in events
Working on #2: remove typed node properties
Working on #2: remove implied type properties
Working on #2: expand added resource node
Fixes #2: unregister from removed subjects