Make it locally testable

[aurium]

• Use .env for local configuration and compatilibilit with Heroku and other hosts;
• The Mongo connection is configurable;
• Client side script know it is in dev mode;
• Adds a basic memory session inplementation;
• There is an step-by-step doc;
• Some ES6 beaulty.

[rafaelcastrocouto]

Thanks a lot @aurium