Copy files not needing muxing during directory processing

[PetrVys]

For purposes of updating the whole photo library, it'd be useful to copy all files from source to destination directory, even ones not needing to be muxed. This should remove the need to use in-place muxing, which is quite dangerous and in case the script hangs during processing (which ExifTool sometimes takes care of!), it can leave photo library in inconsistent state.