title: angular 5 reactive forms, disable validation
body: <p>Currently I have a <code>input type="text"</code> with ReactiveForms.
  Angular always adds <code>ng-xxx</code> css classes (e.g. <code>ng-valid</code>)</p>
  
  <p>I'd like to disable this all together (I know I can just change the appropriate css classes)</p>
  
  <p>Is it possible to disable validation completley (including css etc.) for a single input field?</p>
  
  <p>see <a href="https://stackblitz.com/edit/angular-fjmyzc" rel="nofollow noreferrer">https://stackblitz.com/edit/angular-fjmyzc</a> for an example</p>