add lastname, firstname and admin fields to user model
configure devise; update views and application controller to accept user's first and last name
add admin verification to categories controller
add product validations
add average_rating method to product model
add category validation
modify valid_attributes in products controller spec so that they pass newly added product validations
add correct user checking in controller for actions modifying products; fix specs testing these actions
add path to products' index
update Gemfile for Heroku
add 'author' method to ReviewDecorator