Use new node-txstatsd package for statsd logging

Our custom statsd logger didn't actually work properly. I didn't feel like
debugging it, so I extracted https://github.com/wikimedia/node-txstatsd from
OCG (which works) and plugged it into restbase. Along the way I also cleared
up the metric names slightly, and fixed a name clashs between the option
method & the internal _options property.
Bump up node-txstatsd dependency
Merge pull request #55 from gwicke/master

Use node-txstatsd package for statsd logging