Transition topics into Page objects #1720
Description
Topics have their own page but aren't currently Page. This is weird. It means they don't have all the fields that a page should have such as meta data. It also means it doesn't interact well with the rest of wagtail. We have to hyperlink to topics with external links (saved as url instead of page id, meaning if topic slug changes, link is rotted), we have to render CMS previews custom, and probably other stuff. Manual migrations like this are pretty annoying so probably something for the summer.