That is, if you're browsing a trade list and you go "oh actually, I _do_ want that!", and click the item page to mark it, then click Back, we'll now update the matching stuff on the trade list page to reflect that it's now a match.
This was just a matter of simplifying the GraphQL query, I think the `currentUserOwnsThis` and `currentUserWantsThis` fields just didn't exist at the time?
We _don't_ yet update your _own_ trade list, if you click through to an item to remove it or something like that. The cache update function isn't too tricky, but it's a bit verbose to implement in Apollo, so I'm not bothering right now!
