Added persistence of tasks by using HTML5 Web Storage

    Created a TasksRepository class to abstract the app from
    the Web Storage API. The TasksViewModel uses the repository
    to save, update, retrieve and remove tasks from the browser
    local storage.

    Added a new spec TasksRepositorySpec with unit tests for the
    repository.
Merge branch 'master' into gh-pages
Published version with persistence of tasks via local storage