A Lagom service router.
This trait doesn't add anything, except that it makes the router created by the LagomServer
strongly typed. This allows it to be dependency injected by type, making it simple to use it
in combination with the Play routes file.
For example, if using a custom router, the Lagom router could be routed to from the routes file
-> / com.lightbend.lagom.scaladsl.server.LagomServiceRouter