!act,rem,clu #3549 Simplify and enhance routers

* 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 Nozzle 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

first routing2 prototype

add Resizer

first remote, withFallback and resizer mess

Nozzle and Pool, ActorSelectionRoutee

cluster router

stopRouterWhenAllRouteesRemoved

routing logic in ordinary actor

management messages

cleanup

Scatter gather