[WIP] update for AngularDart 1.x

@kwalrath could you please review when you are available.

/ref https://github.com/angular/angular.dart.tutorial/pull/131
the last two lines are unclear and a bit grammatically complicated. Maybe:

...names, as an HTML element can be associated with only one component.
OR
...names, because only one component can be associated with any HTML element.