Exclude Commons logging and Log4j from dependencies

Sagan is set up with Logback as the logging framework, with Slf4j bridges from Commons logging, log4j and Java Util logging. Prior to this commit both log4j and Commons logging were included in the dependencies. Commons logging seem to get routed fine to Slf4j, but with libraries using Log4j or JBoss logger (used by Hibernate) it seem to be random due to class loading order (mostly not).

This commit exclude both Log4j and Commons logging from the dependencies.
Merge pull request #373 from bjornerik/logging-cleanup

Exclude Commons logging and Log4j from dependencies