Integration with Maven Artifacts API.

Hi!

I was looking for retrieving some info about a Maven Project from a build (like the artifact's version number) when I came up with the `mavenArtifacts API`. I've added connectivity support to this API to the `JenkinsServer` interface and, in consequence, built 6 more model classes to support this new feature. 

Usage:

```java
// get a reference from the Jenkins Server.
JenkinsServer jenkinsServer = new JenkinsServer("url", "user", "password");
// what's your job?
MavenJobWithDetails job = this.jenkinsServer.getMavenJob("my-job-name");
// get the maven module
MavenModule mavenModule = job.getLastBuild().getMavenModule();
// show then the last version.
System.out.println("Last version from the last build: " + mavenModule.getModuleRecords().get(0).getPomArtifact().getVersion());

```

Worked fine for my needs. I hope it became useful for someone.

Thanks for your job!