Install devise and run devise:install.
Generate devise Physical/User.
Add tests of sign up,sign in and sign out.
CanCan installed for authorization. 'admin', 'corrector' and 'student' roles were created.
Fix default value of User's roles.
Implement user management feature for admin.
Fix update user. Blank password key is ignored.
Add user name.
Delete 'cancel button' for destory user.
Fix student access. Students must not be access corrector pages.