See https://www.mediawiki.org/wiki/Requests_for_comment/Multi-Content_Revisions and https://phabricator.wikimedia.org/tag/multi-content-revisions/ - [ ] implement [content handler](https://www.mediawiki.org/wiki/Manual:ContentHandler) stub (with `contentmodel == wikitext` assertion) - [ ] update database schema: MW 1.31 introduced new tables: actor, comment, slots, slot_roles, content, content_models
See https://www.mediawiki.org/wiki/Requests_for_comment/Multi-Content_Revisions and https://phabricator.wikimedia.org/tag/multi-content-revisions/
contentmodel == wikitextassertion)