Define a record type and mapping to schema type, as an alternative to tagging

[hlship]

Especially now that tagging involved a new wrapper type, rather than meta-data, it's gotten a bit intrusive.

With a little more declaration in the schema, we could relate a GraphQL object type to a Clojure record type (or even Java class).

This would allow Lacinia to inuit the object type when dealing with a union or interface type.