Add theme image

I will turn this into a patch later.
This is a straight port of d7 theme_image. however without ability to validate/create image path (what core does in php), what you pass here is what will be used for image.path.

/**
 * Implements JS version of core's theme_image:7. Return a themed image.
 */
Drupal.theme.prototype.image = function(image) {
  var path       = image.path || '';
  var alt        = image.alt  || '';
  var title      = image.title || '';
  var attributes = image.attributes || '';

  attributes     = Drupal.drupalAttributes(attributes);
  return '<img src="' + path + '" alt="' + Drupal.checkPlain(alt) + '" title="' + Drupal.checkPlain(title) + '"' + attributes +' />';
}