Allow Elasticsearch URL to be set by Dockerfile with fallback

[BretFisher]

Story: Someone can set the ES URL via docker-compose with environment variable ELASTICSEARCH_URL. If they don't set it but still launch with Docker, the Dockerfile will fallback to http://hercules.code4hr.org:33366/. If they don't use Docker for development, the app will fallback to this json.

• update Dockerfile to use proper url
• update connectDatabase() to try and use the environment variable if it exists, else fall back to Hercules.json