Delete empty image folders when MB3 deletes the last file from them

[cracksloth 28]

If a user deletes all backgrounds except one, this will result in an empty "extrafanart" folder (when XBMC naming compatibility mode is turned on). In this case, it would seem appropriate that MB3 delete the folder at the same time as it was deleting the last image used from that folder. A similar approach would be seem appropriate for "extrathumbs" folders if they ever become visible to the image edit page.

Edited November 15, 2013 by cracksloth