Switch to using Angular zone

[hongbo-miao]

Article:
https://github.com/OfficeDev/office-js-docs/blob/master/docs/develop/add-ins-with-angular2.md

Issue:
The notifications to update the DOM occasionally do not fire is because the codes run out of Angular zone. A good practice is putting that part of code in the zone, instead of forcing the update.

this.zone.run(() => {
  // ...
});

I will add a PR soon when I get time.

[hongbo-miao]

#997