Use publish/subscribe across multiple Play instances

[wsargent]

There's an example of a chat client using cluster pubsub here

https://github.com/typesafehub/activator-akka-clustering/blob/master/src/main/scala/chat/ChatClient.scala

We should leverage the example, converting streams into actors using

http://doc.akka.io/docs/akka/2.5.2/scala/stream/stream-integrations.html

to demo chat existing across multiple machines.

[wsargent]

Should reference https://github.com/playframework/play-socket.io/tree/master/samples/scala/clustered-chat