picopt could use a --preserve option

When compressing 10 to 20 year old photo collections, I don't want their attributes like time changed. I want the files to be the same, only smaller. The --preserve option usually controls this. I see this from 'man cp': ``` -p same as --preserve=mode,ownership,timestamps --preserve[=ATTR_LIST] preserve the specified attributes (default: mode,ownership,time‐ stamps), if possible additional attributes: context, links, xattr, all ``` Preserving the mode and ownership are important too, so that other users can access the files after shrinkage.