Hubot for notifications

Because PR https://github.com/github/janky/pull/72 hasn't been merged yet and introduces some backwards-incompatible changes, we decided to implement this feature in a more simple way. 

This PR changes the `room_id` database fields to a string so we can use string values for rooms (IRC). It adds a chat service for Hubot (based on https://github.com/francois2metz/janky, kudos to @francois2metz) and doesn't change much of the existing code base.