Implement RoutingService

[paulrayner]

This is the service that translates the network graph to an itinerary.

This could start out by being a fake implementation (based on canned available routes throughout each month or something). Later the Pathfinder app needs to be implemented. Perhaps the routing service could call out to a separate REST API for Pathfinder, or use DCELL (Distributed Celluloid.IO) to do in an async manner.