correct the validatePresenceOf function in comments_new_controller and post_edit_controller
add admin user in seeds.rb
correct setting of tag list in posts_new_controller's save function
make display of category names in templates post_index and post_in_list depend on the categories' existence
create categories_new_controller
create new category view and template
create category_edit_controller
create category_edit_view
adapt posts.feature to changed post model
add redcar files to .gitignore
correct posts_new_controller's validatePresenceOf method
make the select in the post form work (preliminary solution)
make a category's postCount react to posts changing category