title: Angular 2 - Add submitted form flag to FormGroup
body: <p>Is there anyone who have tried to add a property to the FormGroup class. I want to add a submitted property that will be set on the submit of the form because I want to show form errors only after submit. The easiest way is to add a variable in the component that will be set to true on submit, but I don't like this. </p>
  
  <p>If we extends FormGroup, would it be possible to do something?</p>
  
  <p>Thanks you!</p>