Feature Request: Relay support

Description

Add support for conveniently building Relay spec compliance server.

SodaRelayNode Traits and GraphQL Interfaces.
SodaRelayConnection Abstract class.
SodaRelayEdge Abstract class.
SodaPageInfo Abstract class.
SodaQuery's node field shorthand.
SodaRelay Abstract class combining all given abstract classes to automatically create a full Node, Connection, and Edges.