Add authentication and User model

* Add User model
* Add SessionsController
* Add password authentication on User
* Request authentication for all actions except sign in
* Add some helpers for ApplicationController
* Update features to work with mandatory authentication

app/models/session.rb

@@ -0,0 +1,2 @@
+class Session < ActiveRecord::Base
+end

app/models/user.rb

@@ -0,0 +1,11 @@
+class User < ActiveRecord::Base
+  validates_presence_of :email
+  validates_presence_of :password
+
+  def self.authenticate(email, password)
+    user = find_by_email(email)
+    return false if user.nil?
+    #FIXME use bcrypt
+    return user if user.password == password
+  end
+end