Add support for pmd eclipse plugin 4.0.0

This pull request upgrades the pmd eclipse plugin version to 4. Currently, if you have used this version with m2e-code-quality, you'll get a "ClassNotFoundException" for `net.sourceforge.pmd.RuleReference` as this class was moved to a different package.

Internally, pmd-eclipse-plugin 4 uses PMD 5, which works slightly different. I've adjusted the configurator accordingly. Please note, that this works only with the brand new pmd-eclipse-plugin 4.0.0.v20130510-1000.

Finally, added a first PMD test project.

Btw. - the [update site of pmd-eclipse-plugin][pmd-eclipse] is now a p2-repo, so I use this directly.

[pmd-eclipse]: http://pmd.sourceforge.net/eclipse