[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?
Since these are gitignored, can you explain what's in them? (Or better yet, document them somewhere, e.g. in the readme or contributing.md.)

In particular, I see that there's an encrypted version of secrets.yml, but none for vars.yml, so what's vars.yml?