ActorSystem in the CouchbasePlugin uses default configuration instead of couchbase.actorctx

The ActorSystem within the CouchbasePlugin is initialized with the toplevel configuration of the Play application, in contrast to the couchbase.actorctx subpath used by the ReactiveCouchbaseDriver by default. This means the default `application` ActorSystem of Play can't be configured separately, which leads to issues especially when trying to enable Remoting/Cluster with a fixed port (the application crashes on startup with "Address already in use", as both ActorSystems try to listen on the same port).
I've also raised the version to 0.4-SNAPSHOT as others might need to move their ActorSystem configuration to the correct couchbase.actorctx path