Include all lightbox2-helper-images as data x2

Include the 4 images next.png, prev.png, loading.gif and close.png into the respective files.

* Except for loading.gif this hardly increases file-sizes
* Decreases the amount of http-requests+related delays
* Never again any button is missing because of wireless-fuck-ups or 404s.
* Makes it even easier to include lightbox as you don't have to edit any configuration or use absolut paths if you use lightbox from different directories/sub-domains
* Easier upgrades! You can keep the lightbox-directory as-is and just copy it to /lightbox on you server

This is the rebased version of #25