Move bot settings (credentials, post frequency, etc.) to database

[livercat]

Create a Config class that accepts a DB instance. Config values should probably be cached properties on Config.

[decobots]

The preferred method of keeping passwords/api keys secret on heroku is to set config values via the heroku commandline application. https://softwareengineering.stackexchange.com/questions/163506/how-does-one-handle-sensitive-data-when-using-github-and-heroku