REST related mods that use web.xml

merge changes required to load a web.xml and application named in the web.xml. Currently web.xml is hardcoded in ServingLayer.java but should probably be specified via a config param.
Hm - this results in 
Exception in thread "main" java.lang.NullPointerException
	at com.cloudera.oryx.lambda.serving.ServingLayer.makeContext(ServingLayer.java:218)
	at com.cloudera.oryx.lambda.serving.ServingLayer.start(ServingLayer.java:97)
	at com.cloudera.oryx.serving.Main.main(Main.java:30)