Adding docker files to be used by a teamcity build.

Note: secrets.js will need to be manually created on the eventual prod server

Review files and assess if this is ok for teamcity deployment, in particular please advise on any preferred approaches for maintaining a secrets.js. We will end up using a similar approach for alias-server

To test it locally:

1. cp secrets.sample.js secrets.js
2. Update secrets.js

docker build -t herald_local .
docker run --init --rm --name herald herald_local

and msgs send with your specified bot to your specified channel as blocks come in