* also support for serialization of exceptions, see
comment in reference.conf
* extract Throwable and Payload methods to helper classes
* add security checks before creating instance from class name
This is to ensure Akka Cluster Client will work with Java Serialization turned off.
However for the sake of backward compatibility, the protobuf serialization for `akka.actor.Identify`
and `akka.actor.ActorIdentity` is turned off.
- created new subproject akka-protobuf (and added COPYING and LICENSE)
- renamed com.google.protobuf -> akka.protobuf everywhere
- also added such renaming step to the results of protoc compilation in
project/Protobuf.scala
- had to include transcriptions of Netty’s ProtobufEncoder/Decoder to
make multi-node-testkit compile again
