remove superfluous function onSave from comments_new_controller
generate category model and categories controller
add validation to category model
add column category_id to table posts
establish 1:n relationship between models category and post
add categories to seeds.rb
simplify transition after successful update in post_edit_controller
add category routes to routes.rb
add category routes to router.js
add pluralization rule for "category" to RESTAdapter
create category serializer
add link to category index page to header (for both layouts)
adapt posts controller, post serializer and post.js to new relationship with category model
create category-related controllers
create category.js
create category-related ember routes
create category-related templates
create category-related views
add category-related CSS rules
change post.js' formattedDate function to work with undefined objects