Use new GraphQL interface

[joshprice]

New interface using keyword lists will be introduced in graphql-elixir/graphql#82 we need to use that and deprecate old interface.

[bringking]

@joshprice any status on this, or are you looking for help to get it implemented? It seems this work is needed to send errors to the client in the GraphQL response. That is sorely needed to make this spec compliant