Class inheritance support

Add a provider to each derived component, aliasing the base component to the derived component:

@Component({
  selector: 'child-comp2',
  template: '<div>child component #2</div>',
  providers: [{provide: BaseComponent, useExisting: forwardRef(() => ChildComponent2) }]
})
export class ChildComponent2 extends BaseComponent {
}

@Component({
  selector: 'child-comp1',
  template: '<div>child component #1</div>',
  providers: [{provide: BaseComponent, useExisting: forwardRef(() => ChildComponent1) }]
})
export class ChildComponent1 extends BaseComponent {
}

Plunker: http://plnkr.co/edit/5gb5E4curAE2EfH2lNZQ?p=preview