I should be able to concatenate unrelated Lists

(User Story, Closed -> Fixed, Priority: Critical, Test Status: No automated tests yet , Reported By Justin du Coeur, )

Summary: Sometimes I have multiple Lists from very different sources, but they are the same Type, and I would like to display them together.

This is basically _concat(List 1, List 2, List 3...).

Note that we don't need the ability to concatenate a received List of Lists, because that isn't currently possible. Querki's type system is intentionally very simplistic, and Collections always directly contain a Type, never a Collection. (In practice, we only have flatMap, not map.)