add attributes teaser and author_id to table posts
adapt post model to new attributes and establish relationship with user model
change author_id to user_id to avoid unnecessary trouble in ember.js
adapt posts controller to new attributes
adapt ember.js post model to new attributes
adapt and extend seeds.rb
add further CSS rules for authentication index page
create ember.js user controller
create ember.js users controller
generate users controller
add relationship with user model to comment model
adapt post serializer to new attributes
adapt user and comment serializers to the relationship between the corresponding models
add some (mostly post-related) CSS rules
prettify (or at least complicate^^) the layout of the post index page
install gem cancan (preliminary)
create ability.rb for cancan
move class post from post_in_list template to corresponding view