=all #13783 replace protobuf dependency by embedded version

- 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

LICENSE

@@ -18,3 +18,9 @@ the License.
 
 Licenses for dependency projects can be found here:
 [http://akka.io/docs/akka/snapshot/project/licenses.html]
+
+---------------
+
+akka-protobuf contains the sources of Google protobuf 2.5.0 runtime support,
+moved into the source package `akka.protobuf` so as to avoid version conflicts.
+For license information see COPYING.protobuf