Add cancancan to gemfile.
Add ability file and load_and_authorize_resource.
Add role? method to user model.
Add comment explaining line that sets comment's user in comments controller's create action.
Add audio_tag to show existing song on existing track edit view.
Change password fields to use password field element.
Add ability file with some permissions.
Add method to check if user is admin.
Migration: add role column to users table.
Add role to user's attr_accessible.
Add rescue condition for CanCan::AccessDenied to application controller.
Add ability for users to update themselves.
Migration: add cover image to tracks.
Add cover image to index, show, form and attr_accessible for tracks.
Add CoverImageUploader.
Redirect to page user is on if login fails (since login form is on every page).
Users can now manage tracks they own and everyone can read all tracks.
Change width of cover images in tracks views to 300px.