OAK-676: Unify and upgrade SLF4j and Logback versions

Work around the SLF4J warning from https://issues.apache.org/jira/browse/FELIX-2492

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1483262 13f79535-47bb-0310-9956-ffa450edef68