Statsd sink

the codahale stats adapter is copied from https://github.com/organicveggie/metrics-statsd as they [don't have a build available for version 3 right now](https://github.com/organicveggie/metrics-statsd/issues/8).

this sink allows us to report all built-in stats to datadog using the local statsd with this configuration:

```
# conf/metrics.properties
*.sink.datadog.class=org.apache.spark.metrics.sink.StatsdSink
*.sink.datadog.host=127.0.0.1
*.sink.datadog.port=8125
*.sink.datadog.prefix=SPARK
``` 

all the names and namespaces are spark specific. if we want to change that, we need to patch spark.

this is an example of what it looks like in datadog:

![screen shot 2014-03-10 at 16 03 22](https://f.cloud.github.com/assets/48745/2378544/e85031f0-a88f-11e3-8696-6f709a904217.png)

/cc @Shopify/data-engineers