Implementation for netty.

Refactored ws-backend-servlet-blocking code to move common response generation code to a utility class.
Netty implementation has a few issues:

1) If keep-alive for the backend mock is not set for sockets then the implementation fails fast if there are no readily available connections.
2) Netty client does not re-connect if at startup the backend is down
Added documentation.

Also, handler backend restarts & unavailability on startup
Merge pull request #1 from NiteshKant/master

ws-impl-netty implementation