Updated to Akka 2.2.3, added sbt build Project

Hey, I stumbled upon this example while searching for an akka remoting example.
I updated it to Akka 2.2.3 and gave it an sbt project build file.
The build file makes copying the _common.jar_ into the other two projects unnecessary, since these now directly depend on the _Common_ project.
I updated the _README_ accordingly.
Akka 2.2.3 seems to have required you add `.tcp` to the remote protocols everywhere, I did that as well.