Fix broken $scope access

`ng-include` creates it's own scope, so probably the issue that I found comes from the fact that the new "todo" model is not yet created and available when the `MainCtrl` controller gets created, thus the code is unable to access it properly via `$scope` as it is not bound to it.

https://github.com/angular/angular.js/wiki/Understanding-Scopes
http://stackoverflow.com/questions/11412410/angularjs-losing-scope-when-using-ng-include