(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.
Merge branch '2.x' of https://github.com/Netflix/eureka into 2.x
Added stub implementations for EurekaService & ServiceChannel.

The abstractions between the protocol and the server side are not in sync so leaving a lot of stubs.
Merge pull request #168 from NiteshKant/2.x

(WIP) Introducing the concept of EurekaService and ServiceChannel.
Initial proposal for DeltaInstanceInfo