title: Firebase Angularfire2 - listening on queried list child added
body: <p>I'm wondering if it is possible to use "child_added" event with queried lists. Like so:</p>
  
  <pre><code>this.curUserPosts = this.af.database.list('/posts', {
      query: {
        orderByChild: 'user/id',
        equalTo: id
      }
    }).$ref.on("child_added", (child) =&gt; {
       console.log(child);
    });
  </code></pre>
  
  <p>I'm interested in the following here:
  Would it work at all. Would it properly fire only when added child corresponds to the query. How performant it is.</p>
  
  <p>And also, what is the preferred way to handle such queried lists in firebase?</p>