use url helper form book's resourceful routes
use common form for both new and edit book pages
add scaffolding category
remove unused json responses from categories controller
apply one-to-many association to Category and Book models
add foreign key category_id for books
update book's spec to include category association
make all book specs pass again
add model validations for book
make books controller consist with categories controller
move flash message to application layout
install twitter-bootstrap-rails gem
apply bootstrap fluid layout for application
change navbar and sidebar links, and footer
modify books' views to consist with scaffold