refactor(Guards): Re-implement guards feature to use services

[MikeRyanDev]

Before we used provideGuard to quickly create guard factory functions. In order to play better with the offline compiler, this changes guards to instead use traditional services.

BREAKING CHANGE:

Before:

  const auth = provideGuard(function(http: Http) {

    return function(route: Route, params: any, isTerminal: boolean): Observable<boolean> {
      return http.get('/auth')
        .map(() => true)
        .catch(() => Observable.of(false));
    };

  }, [ Http ]);

After:

  @Injectable()
  export class AuthGuard implements Guard {
    constructor(private http: Http) { }

    protectRoute({ route, params, isTerminal }: TraversalCandidate): Observable<boolean> {
      return this.http.get('/auth')
        .map(() => true)
        .catch(() => Observable.of(false));
    }
  }

[brandonroberts]

LGTM