Add missing files

[okaufmann]

Folder assets/stylesheets should contain this images:

• fancybox_loading.gif
• fancybox_loading@2x.gif
• fancybox_overlay.png
• fancybox_sprite.png
• fancybox_sprite@2x.png
• blank.gif

[thegcat]

See #59.

[okaufmann]

Haha lol this is 8 month ago :D

Anyway: sorry I forgot to close this issue as i fixed it for myself...

Thanks ;)