RELAY2: Allow for load balancing for received messages among the local cluster

I've prototyped a configuration option that load-balances applying the changes from a remote SiteMaster across all local nodes in a cluster.

There is still a single SiteMaster (thereby not breaking the existing JGroups model); the difference is that the messages are now forwarded to other nodes in the local cluster and delivered to the application layer there for unmarshalling and processing.