Preserve file metadata when exporting

[Tooa]

• Use copy2 instead of copy when exporting documents. This preserves documents metadata

• Useful when the export dir is used to rsync files to a remote host for offsite backups. The function copy2 makes sure the modification date does not change when exporting on a regular basis. Otherwise, rsync copies all files to the target even if they already exist on the remote. One can work around this behavior with --ignore-existing, but I think copying metadata for backups with the export functionality is important.

Shell we do this for import_documents too?

[MasterofJOKers]

Sounds like a good idea, even though probably more expensive on slow devices, because of the additional lookups and writes.

I'm in favor of doing this for the importer, too, even though the only use-case would be re-exporting again, I guess.