Updated logging to log4j2

With BC still on the Java Logging, it looks incredibly inconsistent with the log4j that all the other mods are now using. To clean that up, I've updated the logging to log4j2, which is the logging method that all mods on 1.7+ are using. I thought that the 6.1.x branch was the best bet, as pushing an update to the other ones just for a logging update seemed silly. But it's up to you.