Align GraphQL resolvers to resolver interface of the GraphQL gem.

[myronmarston]

The GraphQL gem has a resolver interface involving a call method with 5 arguments. We had our own interface that was slightly different. I'm working on optimizing our GraphQL resolver implementation where we just pass a map of resolvers to the GraphQL gem and allow it to dispatch each field to the appropriate resolver. This is a step in that direction.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}