The thumbnail-feature for directory-icons

[mostly harmless]

Displaying 4 thumbnails for the directory icons is a nice idea.
It does not show any thumbnails (yet) if there are no pictures in the folder but in subfolders.
That is probably something for a future version.

I would also prefer to have 1 thumbnail instead of 4 and which changes every 1-2 seconds (sort of browsing the directory`s contents).
Don`t know how good this would be in reality but I think it might be a nice feature.
The image selection here should be random.