Adds authentication through GitHub

This adds authentication through GitHub (using `omniauth` and `omniauth-github`), as well as Twitter Bootstrap (used for the top navbar displaying the current user)

![ci - logged out](https://f.cloud.github.com/assets/605293/531951/28cc5f3a-c13f-11e2-94f7-afdf6efc4652.png)

![ci - logged in](https://f.cloud.github.com/assets/605293/531954/2dbe82f2-c13f-11e2-8aa7-ba6070f8fc88.png)


Specs are probably broken though...