Added TbImageGallery widget

Use: 
```php
    <?php $this->beginWidget('bootstrap.widgets.TbImageGallery'); ?>
        <a href="http://placekitten.com/500/500" title="kitten" data-gallery="gallery">
              <img src="http://placekitten.com/250/250" rel="list-gallery" />
       </a>
       <a href="http://placekitten.com/500/500" title="kitten" data-gallery="gallery">
              <img src="http://placekitten.com/250/250" rel="list-gallery" />
       </a>
    <?php $this->endWidget(); ?>
```