This is an API breaking change if someone implemented their own Routers.
The change is required because the router must know if the local routees
should be started or not so it has to check the roles of the cluster
member (the local one). We could delay this decision of starting local
routees, but that would allow messages to be dead-letter-ed (bad).
* Separate routing logic, to be usable stand alone, e.g. in actors
* Simplify RouterConfig, only a factory
* Move reading of config from Deployer to the RouterConfig
* Distiction between Pool and Group router types
* Remove usage of actorFor, use ActorSelection
* Management messages to add and remove routees
* Simplify the internals of RoutedActorCell & co
* Move resize specific code to separate RoutedActorCell subclass
* Change resizer api to only return capacity change
* Resizer only allowed together with Pool
* Re-implement all routers, and keep old api during deprecation phase
* Replace ClusterRouterConfig, deprecation
* Rewrite documentation
* Migration guide
* Also includes related ticket:
+act #3087 Create nicer Props factories for RouterConfig
