Add User model
Add User model annotations
Add validation of fields for User model
Add User length validation for name field
Add validation for User#email
Add User email validation for uniqueness and case_sensetivity
Add an unique index to User table
Add a before_save callback to downcase user's email
Add bcrypt-ruby to handle password hashes for users
Add password_digest field to users table
Make a basic user model (including secure passwords)
Add an spec for email downcase before saving
Refactor: User callback before_save. #631