Add classes for automatic styling

Thanks for this great module.
I wanted to have some classes on the inserted images, so I could style them by adding some css rules (float: left; margin: 10px 10px 10px 0;) to my stylesheet. I made a small change to the js file, so two classes are added: 'eii' and 'imagecache-[preset]'. This creates output like this:

<a rel="lightbox[eii]" class="eii imagecache-thumbnail" href="/files/myimage.jpg">
  <img class="eii imagecache-thumbnail" title="myimage" alt="mydescription" src="/files/imagecache/thumbnail/files/myimage.jpg"/>
</a>

I attached the patch; I hope you will find this usefull.

By the way, this patch only allows for 'automatic' classes. I think it would be nice in the future if we could have a text field on the easy image insert form, where we can add custom classes per image... But I should probably create a separate feature request for that.