title: Listen to Semantic UI form validation errors before submit
body: <p>Using Semantic UI form, modal and validation, I have a form in a modal and I do not want the modal to close if the form is not valid (which happens when submitted).</p>
  
  <p>The only way I can stop the modal from closing is to add a <code>disabled</code> class to the submit button.</p>
  
  <p>I want to listen to the form (in real time) and toggle the <code>disabled</code> class on and off depending on the current form validation state.</p>
  
  <p>I can only get it to work once the form is submitted but not in real time</p>
  
  <pre><code>$('#myForm')
      .form({
          title: {
              identifier  : 'title',
              rules: [
                  {
                      type   : 'empty',
                      prompt : 'Please enter a title'
                  },
                  {
                      type   : 'length[2]',
                      prompt : 'At least 6 characters'
                  }
              ]
          }
      },
      {
          onSuccess: function() {
              $('#submit').removeClass('disabled');
          },
          onFailure: function() {
              $('#submit').addClass('disabled');
          }
      }
  );
  </code></pre>