Ban aggregate OSGi artifacts

According to http://docs.osgi.org/artifacts/

.. it is generally recommended to use the individual artifacts, as this allows for more precise versioning. In particular, avoid using the osgi.cmpn artifact. After Release 7, the osgi.cmpn artifact is no longer published to Maven Central to encourage the use of the individual artifacts.

In addition to those aspects, using the individual artifacts keeps the class path leaner (particularly relevant for transitive dependencies).

To enforce migration we should ban the osgi.cmpn and also the osgi.core artifacts via a Maven enforcer rule.