Revert "Refactor session view/controller so that form_tag is used insted of form_for"

This reverts commit d17e2e9386a7ae7cea95ae9add649e33a845957d.
Add initial Edit page test/action/view
Add Setting link
Implement the case for update success plus some bug fix
Implement the case for update success plus bug fix

- Implement update action/view for update success.
- Fix the bug that causes errors in rspec.
Implement the case for update success in test/action
Authorize edit/update action in Users controller
Authorize edit/update actions so that unauthorized user cannot access other page
Implement friendly-forwarding on create action in Session
Implement index on Users (test/action/view/helper)
Add rake task to populate fake users with faker gem
Add will_paginate gem for pagination
Add pagination to User index page (test/action/view)
Refactor User index page with render method
Add user destroy feature

- Migrate db to add admin field to User model
- Add destroy feature, considering mass-assignment
- Update spec files including factories, view, controller
Prevent user deletion by sending DELETE request
Merge branch 'chapter9'
Merge chapter9 branch to keep master latest