Deploy to Heroku button

[anishathalye]

Do you think it would be helpful to have a deploy to heroku button (e.g. {link})?

To make this not a pain to use, we'd need to add support for using environment variables in addition to the config.json (should be fairly straightforward), because ideally people should be able to set this up using only the Heroku web UI. Besides that, we'd probably want to do something with how the admin account works so people can change the password via config file (so people don't have issues like #1).

I had already written some config code to make this work on Heroku (for 6.S191), though I haven't done the envvar stuff.

If you think this is a good idea, I can start working on a PR.

[anishathalye]

Done in #26