Refactor API URLs to use GlobalConstants and update CORS configurations for production

jambotron-ui/src/app/services/user.service.ts

@@ -2,9 +2,9 @@ import { Injectable } from '@angular/core';
 import { HttpClient } from '@angular/common/http';
 import { Observable } from 'rxjs';
 import {User} from "../models/user.model";
-import {Tutorial} from "../models/tutorial.model";
+import {GlobalConstants} from '../global-constants';
 
-const API_URL = 'http://localhost:8080/api/users';
+const API_URL = `${GlobalConstants.API_URL}/users`;
 
 @Injectable({
   providedIn: 'root'