first implementation of mongo state factory
moved logging in line with the other Eve components
moved constants to the factory class
adding concurrency update checking on mongo states
adapted logging to use java.util.logger
added javadocs comment and corrected logger factory input
adding initialization via YAML config file
Merge pull request #25 from xvronny/mongodb

Thanks Ronny! I've merged this request. Let's discuss coming week if I need to backport it also to the 2.2.1. Would be quite easy, as mentioned before.