Introduce new metric for scaling. Includes upgrade to Jetty 9, since
we are using Metrics for this, which requires Jetty 8 or above. And
upgrading to Jetty 9 seemed like a good idea at the time, too. It was
late so I may come to regret that.

Took the opportunity to tidy up the beast that is AtlasMain.java, too.
Upgrade maven war plugin
Add histograms for metrics
Merge pull request #384 from atlasapi/jetty-upgrade-metric

Change metric for scaling to utilisation: a metric provided by the Java Metric library