title: knockout validation doesn't add hasError class if exclude validationElement binding
body: <p>I have added knockout validation to my model.</p>
  
  <p>This works fine:</p>
  
  <pre><code>//init validation
  ko.validation.init({
      registerExtenders: true,
      insertMessages: false,
      messagesOnModified: false,
      decorateElement: true,
      errorElementClass: 'hasError'
  });
  
  // has required validation for model observable
  self.CompanyName= ko.observable(data ? ko.unwrap(data.CompanyName) : '').extend({ required: true });
  </code></pre>
  
  <p><strong>HTML</strong></p>
  
  <pre><code>//binding
  &lt;span class="inline-edit-view" data-bind="text: CompanyName, validationElement: CompanyName"&gt;&lt;/span&gt;
  </code></pre>
  
  <p>This adds <code>hasError</code> to the invalid element. If I remove <code>validationElement</code>, though, it doesn't work.</p>
  
  <p><strong>Question is</strong>: Why should I use <code>validationElement</code>? It seems counter-intuitive to me. <br/> I already have <code>extend {required: written}</code> for each element and I do not want to write a <code>validationElement</code> binding for each observable.</p>