img@role causes send-to-kindle failures

[eshellman]

ebookmaker uses data-role attributes on img elements instead of role because the current nu validator incorrectly marks these as validation errors. See validator/validator#1599

the EPUB3 validator does it right, but we have reports that having role="presentation" on an img element causes a send-to kindle failure. https://www.pgdp.net/phpBB3/viewtopic.php?p=1368620#p1368620

Should we stop using role="presentation" for EPUB3 files?