include omniauth-facebook provider
start to build out user persistence
basic oauth flow (TODO: create new users)
logout action
fix csrf protection (not needed for login)
use field name 'image' instead, maps 1:1 w/ oauth facebook data
create user via omniauth if doesn't exist for provider + uid
fix ActiveRecord::NotFound if session[:user_id] is an old deleted User
Merge branch 'auth-facebook'