title: Is it possible to 'watch' attributes' changes
body: <p>Is it possible to "watch" for ui changes on the directive? 
  something like that:</p>
  
  <pre><code>.directive('vValidation', function() {
      return function(scope, element, attrs) {
          element.$watch(function() {
              if (this.hasClass('someClass')) console.log('someClass added');
          });
      }
  })
  </code></pre>