Bug 963800: Add New Relic support.

Note: This requires some ENV vars to be set in order for New Relic to receive 
data.

NEW_RELIC_LICENSE_KEY (from NR admin)  
NEW_RELIC_API_KEY (from NR admin)  
NEW_RELIC_APP_NAME (e.g. nucleus.mozilla.org)

The APP_NAME should be different per deployment. Mozilla's convention is to
use the domain name. Just be sure that it's set appropriately on stage and
prod.