Reef-webserver initial check in

Reef-webserver initial check in
Comments and clean up
Tracking Uri classes and tests
Fixes based on review comments

Fixes based on review comments
Update module name for reef-webserver

Rename reef-webServer to reef-webserver
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into httpServer
Replace TrackingURLProvider

This change uses TrackingURLProvider defined in Reef and added
HttpTrackingURLProvider implementation. Three more test cases are added
for the new implementation. Old TrackingUri interface is deleted.
This change also moved HttpEventHandlers  to a seperate class.
After TrackingURLProvider  is moved to reef-common, the dependency on
reef-runtime-yarn should be removed.
Update on review comments

change the constructor of HttpServerImp to inject JettyHandler
Make JettyHandler injectable
Throw RuntimeExcepton from getTrackingUrl in HttpTrackingURLProvider if
UnknownHostException happens
Some private, final fixes
Exception Handling in HttpTrackingURLProvider
Adding failure path to data loading
Added HelloREEF HTTP example
Merge branch 'weimer_http' into httpServer
Added the dependency on reef-webserver
Added the call to setup the webserver
HelloREEFHttp update and pom file change
Adding Hello Reef Http Yarn
fixing data locality bug
Add ReefEventStateManager

Added ReefEventStateManager, registed eventHandlers to catch evaluator
status.
Updated ReefEventHandle to returns the data to the client when it
receives a request. It contains some hard coded string . For now it is
for showing some samples.
merged from master

Code merged fro mmaster
removed httpRequest/httpResponse
updated on review comments

updated on review comments
use injection for HttpServer and code clean up