New Relic initial config

Added New Relic to Bridge following the steps on https://devcenter.heroku.com/articles/newrelic#add-the-new-relic-agent-as-a-scala-sbt-play-2-dependency

(NOTE: This will require additional Heroku configuration to fully set up.)

This adds New Relic as an SBT dependency and adds the basic newrelic.yml config file. (Ideally, most of these configs would be available in the newrelic dashboard, but a few of them are sadly only available in git flat file form.)

This has been tested on a "local" test stack on heroku. We get latency metrics per base URL (root, /api/v1/auth/signIn, etc), and a graph of errors in the 500 family. We'll probably want to set up additional log scans for ERRORs in the log as the next step.

The availability canary can be configured through the dashboard.