adds #testSerializationWithIdentityPreservation showing the problem
adds #testSaveWithIdentityPreservation also showing the problem
fixes(asJSON): the onAboutToJSON method is now obsolete
removes #onAboutToJSON
fix(asJSONString): small serialization fix
increments version
Merge pull request #4 from flow-stack/feature/serialization-preserving-graph-identity

Feature/serialization preserving graph identity