Update requirements with new version of Celery
Merge branch 'celery_update'

* celery_update:
  Update requirements with new version of Celery
Refactor OAuth logins, with a common framework for Facebook and Linkedin

This reduces code duplication and making adding new OAuth2 authentication
providers much easier. Google login will soon be converted to use OAuth2.

Facebook users now store their Facebook ID with SlideAtlas, and user
lookups use this Facebook ID. This allows a user to change their email
address at Facebook without losing access to their SlideAtlas account. If
a Facebook ID is unknown (as it will with existing users logging in for
the first time after this update), lookup falls back to email addresses.

This also improves Facebook login by providing much more robust error
checking and OAuth CSRF attack protection.
Update SlideAtlas roles based upon Facebook group membership

Fixes #11.
Emit 'user_registered' signal upon all new user registrations
Merge branch 'demo_sessions'

* demo_sessions:
  Emit 'user_registered' signal upon all new user registrations
  Update SlideAtlas roles based upon Facebook group membership
  Refactor OAuth logins, with a common framework for Facebook and Linkedin
Showing correct info in about tab
Update status page with better formatting and more information
Merge branch 'status_page'

* status_page:
  Update status page with better formatting and more information
  Showing correct info in about tab