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

features/step_definitions/sessions_step.rb

@@ -0,0 +1,26 @@
+Given /^I am not signed in$/ do
+
+end
+
+Given /^I am signed in$/ do
+  user = Factory.create(:user)
+  visit new_session_path
+  fill_in('Email', :with => user.email)
+  fill_in('Password', :with => user.password)
+  click_button('Sign in')
+end
+
+Then /^I should be redirected to the sign in page$/ do
+  current_path.should == new_session_path
+end
+
+Then /^I should be redirected to the home page$/ do
+  current_path.should == root_path
+end
+
+When /^I submit valid credentials$/ do
+  user = Factory.create(:user)
+  fill_in('Email', :with => user.email)
+  fill_in('Password', :with => user.password)
+  click_button('Sign in')
+end