Supermarket monitors Pull Requests for CLA signage

This is the first part of Curry - a part of the application that checks
the committers of pull requests that are opened insubscribed repos.

Pivotal Tracker Story: https://www.pivotaltracker.com/story/show/64753356

This implements the following:

* Interface for managing the repositories that Supermarket subscribes
  to, which also interfaces with GitHub to create a subscription hook
* Creates an end-point that GitHub sends a POST request to when a pull
  request is updated (opened, synchronize, closed, reopened)
* Checks all of the committers in a pull request, and stores committers
  who have not signed a CLA, identifying those committers either by
  their GitHub login, or if they don't have a GitHub login, the email
  address used to author the commit.
* If all of the committers in a pull request have signed the Supermarket
  CLA, a label is added to the Pull Request saying so.
* If there are users who have not signed a CLA, a comment is left
  instructing those users to do so.

Implementation details:

* Use the Octokit gem to interface with GitHub's API.
* Use VCR for recording and playing back HTTP requests in tests
* Use currybowl for Curry hub callbacks. Only used in Development.
* The checking of PR committers and interacting with the Pull Request
  are handled with Sidekiq background jobs.
Add redis recipe.

The recipe is loosely based off of [phlipper/chef-redis], and at this
point only provides one overridable attribute. For development and
staging this should suffice. We can expand the scope of the recipe as
needed.

[phlipper/chef-redis]: https://github.com/phlipper/chef-redis
Run app services on Vagrant with foreman
Add sidekiq recipe

Like the Redis recipe, the Sidekiq recipe is minimally configurable;
just enough to get something running for now.

When deploys start, we tell Sidekiq workers to stop accepting new jobs.
When we stop our web server, we also stop Sidekiq. When we start the web
server, we start Sidekiq.

At some point, we'll want a process manager to handle some things that
Sidekiq currently does on its own: daemonization, and log redirection in
particular. It'd also be nice to have a monitor to revive crashed
processes.
Merge pull request #84 from opscode/spicy-curry-64753356

Automatically verify CLA status of incoming PRs.