First attempt to OSGI-fy Kundera

pom.xml got a bit messed up because of whitespaces...
What I basically did is added maven-bundle-plugin to generate OSGI Manifest and maven-jar-plugin to include this Manifest. I've done it now only for core module and mongo client. WIll need to be replicated for the rest

In the Core module, I added OSGI Activator and modified PersistenceUnitConfiguration to be able to load persistence.xml from other bundles.