ImproveloggingwhenusingTitanasadependency

Managing the logging dependencies for Titan is a little tricky when using it as a dependency, with several logging frameworks brought in with dependencies. Consider:
- Excluding any log4j, commons-logging dependencies to prevent them sneaking in. Support those logging frameworks with SLF4J bridging modules
- Include the final SLF4J binding in the distribution only (supporting tests w/ test scope modules), allowing the binding module to be chosen without requiring an explicit dependency exclusion. SLF4J will print a nice, friendly standard out message for a developer if they've forgotten a binding
- Consider logback. It's a native SLF4J implementation and far friendlier than log4j

该提问来源于开源项目：thinkaurelius/titan