Add omniauth-identity gem and initial configuration
Add identity model for omniauth
Add a simple route and controller for debugging
Add User model
Build relationship from identity to user
Add some helper method
Redesign auth system
disable some unused middleware
Add login page
Add user controller
Rename usercontroller to userscontroller
Remove omniauth-identity
Use has_secure_password to implement plain auth system
Delete the comments in the route.rb
Add an auth layout for login and logout page
Some small changes on auth routes
Only allow one user exist in this system
Add notice info & only allow one user to sign up
Use four kinds of flash message types.

success for create or update success
notice for info, such as signed out
alert for warning, such as need sign in
error for create or update failed