Add Router as replacement for ServiceResolver

ServiceResolver is just a very bad name. Therefor it needs to be replaced with something that is named after its purpose. The definition of a Router is as follow:

A Router maps a Envelope into a Receiver. A Receiver is a callable and must be returned from the Routers map method. The Router can be Simple like `SimpleRouter` or it could be advanced with wildcards (not implemented). It is important to know the the Router is only for routing inside Bernard and have nothing to do with RabbitMQ or ZeroMQ routing.