title: display form.valid when user can't valid [angular]
body: <p>So. I follow the tutorial on build in validator and form validation on the official doc -> </p>
  
  <p>One of the thing that chock me is that you can't know why you can't submit your form when something is wrong. </p>
  
  <p>Take the plunker exemple they give in the <a href="https://angular.io/docs/ts/latest/cookbook/form-validation.html" rel="nofollow noreferrer">doc</a>:  plunker -> <a href="https://plnkr.co/edit/TJUZlkKOv22PzPB7gHEK?p=preview" rel="nofollow noreferrer">https://plnkr.co/edit/TJUZlkKOv22PzPB7gHEK?p=preview</a></p>
  
  <p>You can NOT click on submit, your mouse turn into a stop signal which is fine and normal.</p>
  
  <p>But you have to check all over your form to find what you missed.
  I hope there would be a way to put a tooltip to show which field was required/falsy to at least explain to the user "something is wrong in what you did, check this particular field (which is paint in red but you look too d*** to understand)'.</p>
  
  <p>Do you have any clue about how to access to <code>form.valid</code> and get some minimal explenation about why the form in not valid.</p>