Should use spree_user in devise_for routes

Fixes #88
Use correct path for routes in shared/_social

Fixes #90

Conflicts:
	app/views/spree/shared/_social.html.erb
Fix route for new_spree_user_registration_url in omniauth_callbacks_controller

Conflicts:
	app/controllers/spree/omniauth_callbacks_controller.rb
Simplify AuthenticationMethod#active_authentication_methods?
Add test ensuring that a sign in flow with Facebook works
Use 1.8 hashrockets for this branch
Use 1.8 hashrocket syntax in shared/_social.html.erb
Use spree_current_user as user variable in view. Fixes crash when viewing accountpage.

Fixes #91

Conflicts:
	app/views/spree/users/_social.html.erb
fix nil related error on edit account page
use spree_current_user to prevent password fields turning up
Fix password fields being visible, test Twitter authentication
added path_prefix preference

Fixes #93
Allow spree_core to handle merging guest orders