Github Commit Count

https://www.pivotaltracker.com/story/show/64891298

* Displays a user's contribution to different projects on profile page
* Introduces a `GithubCommitsJob` which fetches contribution statistics from the Github API using the octokit gem through unauthenticated requests.
* Introduces a rake task which provides a interface to run the `GithubCommitsJob` through `rake fetch_github_commits`.
* The task is supposed to be run every 24 hours through the Heroku Scheduler.

![gcc](https://cloud.githubusercontent.com/assets/1736001/3969985/de181a58-27c5-11e4-9b88-38aecbd46bb9.png)