Update Ember to 1.3.1 and ember data to 1.0.0-beta.6, also jquery, handlebars

In reference to https://github.com/tastejs/todomvc/issues/704

Also a few fixes and improvements @mixonic and I made to make the code more idiomatic:

  * The new-todo input now focuses when the page loads
  * Leverage Ember Computed Properties in the TodosController, removes a lot of extraneous code
  * Add a `{{pluralize}}` Handlebars helper (and remove some HTML from the TodosController)
  * Remove the `auto-save` from the Todo model. The TodoController now handles saving when the todo is completed
  * Small optimization of the debouncing of the call to remove a todo. Instead of debouncing a call to `this.send` (which debounces sending of *any* action), added the `TodoController.removeTodo` method and made the TodoController `removeTodo` _action_ call the method. We debounce the call to the `removeTodo` method explicitly now.
  * javascript dependencies are in `bower_components`