thumbnail tweaks

thumbnail tweaks

* zoom icon dimensions adjusted to the new icon
* div wrapper around zoom icon with class, float on div instead of align on image
* caption as div with class to allow extra styling in future skins
* width set on outer div as well (width + 2)
* using the zoom icon as centered bg image in the monobook css, with a { display: block }
* print css update (class name for caption div instead of p)