fix migration conflict
add administration functionality for User and Book models
change admin model to just user with is_admin being true
reduce admin model, use boolean in User model instead.
Merge branch 'feature/admin' of https://github.com/goooooouwa/book-store into feature/admin
add admin login
Merge branch 'feature/admin' into develop
add book_comments under admin
Merge pull request #34 from goooooouwa/develop

 admin module