add route to display only completed todos
add comments to describe behavior
Clear all completed todos

1) Add behavior that only shows the “Clear completed” button if there
are any completed todos.

2) Dynamically change the count of the completed todos

3) Delete all completed todos
Notes: computed properties example
dynamically check the checkbox when all todos are completed
toggle all todos between complete/incomplete state
Persist data on browser's localstorage

Use the localstorage adapter (written by Ryan Florence -
https://raw.githubusercontent.com/rpflorence/ember-localstorage-adapter/
master/localstorage_adapter.js)

To persist data to the browser
ignore rubymine stuff
Notes: most commonly used helpers in tutorial