Prevent unnecessary requests to NextBus

[elliottsj]

e.g.

query {
  agency(tag: "ttc") {
    routes {
      edges {
        node {
          id
          shortTitle
          tag
          title
        }
      }
    }
  }
}

With routes being a field nested in an agency, GraphQL will first try to resolve the agency before resolving the routes; an unnecessary request to http://webservices.nextbus.com/service/publicXMLFeed?command=agencyList is made when only the agency's tag is required to fetch routes from http://webservices.nextbus.com/service/publicXMLFeed?command=routeList&a=ttc

[elliottsj]

Possibly use https://github.com/facebook/dataloader

[elliottsj]

More discussion: graphql/graphql-js#111