title: How to get the downoladURL from files uploaded with AngularFireStorage referenced in a collection
body: <h2>I'm using Angular v"5.2.0" and angularfire2 v"5.0.0-rc.6"</h2>
  
  <p>I'm uploading images to a storage location using angularfire2, and I'm referencing them to a collection called photos:
  The collection has this structure:</p>
  
  <ul>
  <li>teamName:"teamName" </li>
  <li>path:"storageLocation/fileName.jpg" </li>
  <li><p>size:"4544"</p>
  
  <pre><code>&lt;div *ngFor="let team  of teams |async"&gt;
   &lt;h3&gt;{{ team.teamName }}&lt;/h3&gt;
   &lt;img class="card-img-top" [src]="team.path" width=50px&gt;
   &lt;button class="button is-danger" (click)="close()"&gt;Close&lt;/button&gt;
  &lt;/div&gt;
  </code></pre></li>
  </ul>
  
  <p>The example provided in the documentation says i have to point to the specific locationPath to call the functions to retrieve to downloadURl</p>
  
  <pre><code>constructor(private storage: AngularFireStorage) {
   const ref = this.storage.ref('users/davideast.jpg');
   this.profileUrl = ref.getDownloadUrl();
  }
  </code></pre>
  
  <p>Is there any way to retrieve the downloadURL from a list of documents?</p>