Unable to create new todos - $scope.todo is undefined

While working through the tutorial, I found that creating a new "todo" item was not possible given the way `$scope` is treated when using `ng-include`. I modified all references to `$scope.todo` to `this.todo` in order for the application to work.

https://github.com/angular/angular.js/wiki/Understanding-Scopes
http://stackoverflow.com/questions/11412410/angularjs-losing-scope-when-using-ng-include