WIP - Update GitHub OAuth support

Need to update our GitHub OAuth code to support the newest stuff in https://github.com/atmos/sinatra_auth_github. I've bumped the gem to 0.13.3 but I think there's some configuration stuff and possibly scopes changes that we need to consider.

I know that @atmos has pointed me in the right direction wrt Teams authentication but I'm an idiot when it comes to OAuth. I'm not sure whether we need to support Teams for everyone, just for internal GH use, or what. @brntbeer - you're the project guru when it comes to this, do you mind taking a look at this?

P.S. Here is some logging output from this branch. Note the deprecation warnings.

```
21:54:24 web.1  | 127.0.0.1 - - [11/Mar/2013 21:54:24] "GET /auth/unauthorized HTTP/1.1" 302 - 0.0014
21:54:24 web.1  | [warden-github] Deprecated configuration github_client_id used. Please refer to the README for updated configuration instructions.
21:54:24 web.1  | [warden-github] Deprecated configuration github_secret used. Please refer to the README for updated configuration instructions.
21:54:24 web.1  | [warden-github] Deprecated configuration github_callback_url used. Please refer to the README for updated configuration instructions.
21:54:24 web.1  | [warden-github] Deprecated configuration github_scopes used. Please refer to the README for updated configuration instructions.
21:54:24 web.1  | 127.0.0.1 - - [11/Mar/2013 21:54:24] "GET /auth/github HTTP/1.1" 302 216 0.0059
```