Test and integrate a custom nginx.conf if provided.

On the new platform, uses an `nginx.conf` supplied in the root of a repo by a customer, and either fails or passes a deploy based on whether the fully integrated configuration passes an nginx configtest.

On Cloud, if an nginx.conf is detected, it provides a message informing customer of where custom nginx configuration should normally be placed, but performs no other action. Message can be disabled in `ey.yml` if desired.

This treats nginx.conf as sort of equivalent to a Gemfile or composer.json; something which is tied into an application's deployment workflow.