Callbacks to get information about (de)serialized types

[ManuG85]

Added callback properties to Settings class which get called from the ObjectSerializer before an object gets serialized or deserialized. These callbacks can be used e.g. to log actually used types or to register types on demand. The later can be used when there are two instances of the serializer (because they are in different processes or in a client-server environment) to inform the counterpart about registrations.