Property 'toPromise' does not exist on type 'Observable<Response>'
You need to add the operator like this:
import 'rxjs/add/operator/toPromise';
This is needed for every rxjs operator you want to use.
Try adding 'Response' to your import statement from '@angular/http' like this :
import {Http, Headers, Response} from '@angular/http';
Also i noticed you don't import Ingectable from angular core although you use @Injectable decorator.
import { Injectable } from '@angular/core';
use this import at the beginning
import {Observable} from "rxjs/Rx";