Added thumbnail copyright functions to attachment media in Media library:
- wpc_thumbnail_copyright_holders() – a filterable list of common image copyright bodies
- wpc_thumbnail_copyright_fields_to_edit() – Edit Media fields for copyright override / select
- wpc_thumbnail_copyright_fields_to_save() – Save Media fields
- wpc_thumbnail_copyright() – returns the copyright override / selection
PR: https://github.com/dc-thomson/wordpress/pull/1323