[WIP] Setting up a base new-relic setup using ansible vault

- Fixes #67 

This change also introduces a new `ansible-vault` secrets file, which has our encrypted `new-relic` key. A side-effect of this now you'll always need the vault key to deploy/setup.

Thoughts?
Nice.

Minor q: do we need the `new_relic_app_name` as a separate var, if it's only used here for the `NEW_RELIC_APP_NAME` env?