Audit Heroku env vars to make sure Heroku deploys have all the required variables

[ibrand]

Describe the Situation It's possible that app.json is out of date... I don't think we've updated it in a while and environment variables have changed. All of our Heroku 1-click deploys reference those variables to prompt the admin on which variables are necessary for their deployment. Cross-referencing app.json with the environment variable reference and the current state of the app and ensuring that all the correct required and optional configuration is in app.json should fix this. It might not actually be a problem, but it needs an audit.