Even if "low resource usage mode" is turned on, which says it avoids storing thumbnails to disk to save space, it still stores thumbnails to disk. It just deletes _all_ thumbnails afterwards (even those not from gwenview itself).

This was also kind of racy, because thumbnailwriter could still be running, but the folders would be deleted, so it spammed a ton of error messages.

Doesn't store thumbnails when it shouldn't anymore, doesn't delete thumbnails from other applications nor the thumbnail folders, thumbnailwriter doesn't spaz out during exit, stores thumbnails when it should.