@Override
        public String toString() {
            return "Registration[" + id + " = " + className + ", serializer=" + serializerClassName + "]";
        }
Holds a compiled set of message registration information that
 can be sent over the wire.  The received message can then be
 used to register all of the classes using the same IDs and 
 same ordering, etcetera.  The intent is that the server compiles
 this message once it is sure that all serializable classes have
 been registered.  It can then send this to each new client, and
 they can use it to register all of the classes without requiring
 exactly reproducing the same calls that the server did to register
 messages.

 <p>Normally, JME recommends that apps have a common utility method
 that they call on both client and server.  However, this makes 
 pluggable services nearly impossible as some central class has to
 know about all registered serializers.  This message implementation
 gets around by only requiring registration on the server.</p>

 @author    Paul Speed
jme3-networking/src/main/java/com/jme3/network/message/SerializerRegistrationsMessage.java