Fixes ConcurrentModificationException and NullPointer on heavy load (~2000 request / seconds)
Revert StubbyTestClient to use default binding port instead
Included the start of the StubsPortalHandler.java code inside the try/catch to better troubleshoot concurrent issues on load
Updated JettyFactory.java to init QueueThreadPool with a max of 1500 thread
Xeger static map now using ConcurrentHashMap
Clean some useless comments in StubCallbackBuilder.java and StubCallback.java
Update YamlParser.java,StubResponse.java, StubResponseBuilder.java to have the headers in a ConcurrentHashMap type instead of LinkedHashMap
Fix unit test