Add support for more CodeMeta contexts URLs

Right now, the CodeMeta mapping requires a specific URL as @context, in order to not request contexts from untrusted URLs.

However, the JSON-LD spec allows arbitrary URLs to get the same content; so we should do something about it if we want to support codemeta.json files that are not copy-pastes from the template provided by CodeMeta.

---

Migrated from T1316 (view on Phabricator)