Include multiverse ID in cards in set listing

In `GET /set/:name(/:page)` it might be useful to know the multiverse ID of a card's specific version that is included in that set, without having to parse that card's versions. This is as opposed to requesting a card by its multiverse ID, in which case the multiverse ID is already known; or requesting a card by its name, without caring about a specific version and being able to see all of the versions with their multiverse IDs.