title: ng2-dragula and dynamic form no sync directly
body: <p>I have a form generated dynamically by the user:</p>
  
  <pre><code>  // this._fb is a FormBuilder
    ngOnInit():void {
      this.myForm = this._fb.group({
        message: this._fb.array([
        ])
      });
  </code></pre>
  
  <p>the json generated is something like</p>
  
  <pre><code>{
    "message": [
      {
        "type": 1,
        "value": "first message",
      },
      {
        "type": 1,
        "value": "second message",
      }
    ]
  }
  </code></pre>
  
  <p>I have added the ng2-dragula directive in order to change the messages order</p>
  
  <pre><code>&lt;form [formGroup]="myForm"&gt;
    &lt;div formArrayName="message"&gt;
      &lt;div [dragula]='"bag-one"' [dragulaModel]='myForm.controls.message.controls'&gt;
        &lt;div *ngFor="let c of myForm.controls.message.controls; let i=index" class="panel panel-default" &gt;
          &lt;div class="panel-body" [formGroupName]="i"&gt;
            &lt;label&gt;value&lt;/label&gt;
            &lt;input type="text" class="form-control" formControlName="value"&gt;
          &lt;/div&gt;
        &lt;/div&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  </code></pre>
  
  <p>The drag function is working nicely, however when I'm displaying the json of my form, it's still the old order, except if I start to change the content of a field. I that case the form is updated.</p>