Thickbox class resizes to fit

[feillyne]

The thickbox / lightbox class resizes the image to fit the screen, and the image itself is clickable (to see it in full view), plus a bigger close button?

Also the "Lightbox URL" option in Format options of the WYSIWYG editor should add thickbox class to image URLs not to the images themselves like it is now (adding that class to images does not seem to do anything).