Naive OAuth implementation against GitHub

@dentarg can we use this until we have a better implementation?

I'm thinking that we should stick with OAuth, and look into [Auth0](https://auth0.com/). I'd like to have a working authentication/authorization system in the mean time though.

We could look into [omniauth](https://github.com/intridea/omniauth), but I think we need to figure out some more about this app before we introduce it.