Allow use of environment variables instead of using config.json

[seabre]

If you want to use this in a service like Heroku, keeping config.json in your repo is not desirable.

Modified config.py to check for certain defined environment variables that map to to the required options in config.json.

If all of the environment variables are defined, use the information from the environment variables instead of config.json

If not all of environment variables are defined, try to read config.json.