PyCon Sprints - Adding Registration Page

Works with Twitter and Google OAuth2.

**TODO**

* [ ] @birdsarah - Create Twitter application for authentication ([specs](http://psa.matiasaguirre.net/docs/backends/twitter.html))
* [ ] @birdsarah - Create Google application for authentication ([specs] (http://psa.matiasaguirre.net/docs/backends/google.html#google-oauth2)) 
* [ ] @birdsarah - Create second set of Google and Twitter credentials to add into `local_settings.py.dev` to replace @dlanger's
* [ ] Set up proper values for `SOCIAL_AUTH_TWITTER_KEY`, `SOCIAL_AUTH_TWITTER_SECRET`, `SOCIAL_AUTH_GOOGLE_OAUTH2_KEY`, and `SOCIAL_AUTH_GOOGLE_OAUTH2_SECRET` in `local_settings.py.production`
* [x] Add links with appropriate images to registration page to `/login/twitter` and `/login/google-oauth2`