Use slf4j throughout all stats modules

Some modules, for example ipv6servers, use slf4j for logging, others, bad example hidserv, use System.err/out for logging.

Check all org.torproject.metrics.stats sub-packages and make them use slf4j. Secondly, create an appropriate logback.xml file and adapt the run-java ant-task to use logback logging.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information