Added Lightbox detection

Lightbox is also used by various CMS like vBulletin to display images, as far as I know.
http://lokeshdhakar.com/projects/lightbox2/
https://en.wikipedia.org/wiki/Lightbox_%28JavaScript%29
corrected Lightbox categories

that's more accurate
added Lightbox icon, it's the Favicon of the Lightbox info page. It is *not* the same favicon as the main page hosting the lightbox page has; it's a green version of it, so I think that it can be seen as the "Lightbox logo". It is also so simple that it can't be copyrighted. :-)
Merge pull request #395 from ToBeFree/patch-1

Added Lightbox detection