[Curry] Application receives updates from GitHub PRs, comments on the PR or sets a label based upon the CLA status of the committers in the Pull Request

:construction: 

Curry allows Chef Admins to keep track of GitHub repositories for which Supermarket tracks CLA status. This Pull Request encompasses the initial part of this functionality: subscribing to GitHub repositories, checking the committers CLA status on Supermarket and leaving a comment and/or label based on the results.

Pivotal Tracker ID: [64753356](https://www.pivotaltracker.com/story/show/64753356)

Left to do:

- [ ] add redis recipe
- [ ] add sidekiq recipe
- [ ] use foreman for vagrant