Added support for Jenkins Notification Plugin.

@daspilker could you please review?

Tested with [Notification Plugin](https://wiki.jenkins-ci.org/display/JENKINS/Notification+Plugin) 1.6, but should also work with 1.5.

Syntax:

````
job {
	...
	// see below for possible values
	notification(String url, String protocol = "HTTP", String format = "JSON", String event = "all", int timeout = 30000)
	...
}
````

````
job {
	...
	notification {
		endpoint { // can be repeated to add multiple endpoints
			url(String url) // url to the notification endpoint
			protocol(String protocol = "HTTP") // use HTTP, TCP, or UDP
			format(String format = "JSON") // use JSON or XML
			event(String event = "all") // use all, started, completed, or finalized
			timeout(int timeout = 30000) // endpoint call timeout (in ms)
		}
	}
	...
}
````