(WIP) Introducing the concept of EurekaService and ServiceChannel.

-- A service is the access point for registry access (both read/write)
-- A channel abstracts a protocol/command so that it provides a higher level abstraction of what is to be done for a command.

We can bikeshed on names but lets discuss the abstraction.
At the protocol level we send key/value pairs in the update. On the client side, it means we need to calculate the diff prior to send, and on the server side we have to merge last InstanceInfo version with the received key/value pairs.