image and audio cleanup

Could be a good idea, just like clean cache, to have a button that scans the resources in the books folder and delete whatever is not used. The folders are getting larger and larger whenever one deletes an animation or a bitmap and loads it again. It all duplicates and there's no way to delete the duplicated items. Even if I delete them manually I still see them in the lists of images/audio files I can use, which is confusing.