Add a DirectedGossip struct (#6803)

* Add a DirectedGossip struct

* Move protocol from prototype::new to biuld

* More traits impls

* Explain ordering

* Apply suggestions from code review

Co-authored-by: Toralf Wittner <tw@dtex.org>

* Address concerns

* Add basic test

* Concerns

* More concerns

* Remove QueueSenderPrototype

* Rename

* Apply suggestions from code review

Co-authored-by: Max Inden <mail@max-inden.de>

Co-authored-by: Toralf Wittner <tw@dtex.org>
Co-authored-by: parity-processbot <>
Co-authored-by: Max Inden <mail@max-inden.de>