Update Dockerfile/docker-compose.yml for Convox

[sandeep]

This allows Botmetrics to be run locally and on AWS using Convox Not quite 1-Click but addresses #7

• Changed config/database.yml to database.yml.sample
• Added Convox Images
• Changed db to database so the URLs are correctly injected into the containers
• Removed Volumes for production
• Updated the Readme for Convox instructions

[arunthampi]

This is awesome. LGTM 💯