Add social_auth

To create the tables, run:

    $ python manage.py migrate social_auth
Setup social-auth with Twitter

To make it work, you must set the required settings for Twitter
in you 'local' settings: lumina/local_settings.py

This settings file is ignored by Git, so it should safe
to add TWITTER_CONSUMER_KEY and TWITTER_CONSUMER_SECRET.
Dump user.social_auth.all on home
Add django-social-auth to requirements-travis-ci.txt
Allow (dis)connect Twitter accounts on home page
Add social_auth_by_name_backends to TEMPLATE_CONTEXT_PROCESSORS
Open link in new window
Use 'auth_providers' to check for user auths
Add support to login with Google-OAuth
Add icon to identify Twitter accounts
Remove footer