Added an Authentications table.

Connects users to remote web services, as recommended at
http://asciicasts.com/episodes/235-omniauth-part-1

In addition, we store "token" and "secret" fields.
Stub "authentications#create" method.
Removed unneeded generated files.
Add omniauth to our middleware.
Fix typo in models/member.rb
Fix stub authentications#create method

As per comment at
http://railscasts.com/episodes/235-omniauth-part-1?view=comments#comment_153390
Create an authentication object on successful callback.