use interceptors for GQL response transformation

[fbielejec]

Problem

GraphQL endpoints which return maps have to wrap their response to transform keys into camelCase that fits the graphql schema (example)
It would greatly improve readability and simplify the codebase to have a general mechanism that transparently transforms these responses.

Implementation

The pedestal server allows for the use of interceptors.
And example is already used to inject custom context into the resolvers.
This is one possible solution.

Acceptance Criteria

Interceptor / middleware that transforms responses. Current endpoints cleaned of the clj->gql transformations.

Notes

Lacinia can be used separately from the pedestal server, and it is possible to replace the pedestal webserver with ring or yada if assignee deems it necessary.

Future Steps

Argument and response logging middleware/interceptors : #7