Client side refactoring

-- Introducing a EurekaClientRegistry which feeds to all users of the client.
-- Separated eureka-server, eureka-read-server and eureka-write-server
Our protocol semantic does not require waiting for ack, before submitting another message. For change notifications (which are also acked) this would incur too big round trip delay. For client side messages are sent less frequently, so syncing does not hurt, but do we need it?