Reef-webserver initial check in

This code is to set up http server using Jetty for Reef. The change includes the following components:
 * `HttpRuntimeStartHandler` – it is bound as a RuntimeStartHandler for Clock 
 * `HttpRuntimeStopHandler` – it is bound as a RuntimeStopHandler for Clock
 * `HttpServer` which manages create/start/stop Jetty server. It also creates Jetty handler and registers it to the Server
 * `HttpHandler` – client need to implement its own handler such as ReefHanlfer, NrtHandler, etc.
 * Jetty Handler – it maintains a hashMap of specification and HttpHandler. It routes http request to those handlers. 

The server can be triggered by the test case. The configuration is not merged with Driver Configuration yet.