Add option for disabling the double translation of timer metrics in statsd

When a "Gauge" (in statsd lingo) is sent over, statsd will compute a bunch of trends and percentile calculations for each metric. With Yammer Metrics timers and histograms, those calculations are already there, so there is no need for statsd to calculate them again.

This commit provides an option that allows statsd to just take the metrics as provided by the metrics registry and pass them along to graphite un-altered.

This commit is backwards compatible.

If merged, please kindly perform a new 2.3.1 release to maven central.