title: How to set the focus on an dxi-item
body: <p>We are using DevExtreme-Components from DevExpress in our Angular 6 application. We have a form built with the help of dxi-item elements like this:</p>
  
  <pre><code>&lt;dx-form id="form" #manageOfferForm [formData]="getOfferToManageForView"&gt;
                  &lt;dxi-item class="dx-fieldset" itemType="group" caption="Projektstammdaten"&gt;
                          &lt;dxi-item  dataField="description" [label]="{text: 'Description'}"&gt;
                          &lt;/dxi-item&gt;
                   ...
  </code></pre>
  
  <p>Now my question is how can I set the focus on the dxi-item editor element from the controller?</p>