Network crate cleanups (#3049)

* Remove useless internal messages

* Remove NetworkService::disconnect_peer

* Remove NetworkMsg altogether

* Rename ProtocolMsg ServerToWorkerMsg

* Remove useless code

* Add example for parse_str_addr

* Move parse_str_addr and ProtocolId to config

* Don't reexport the content of config

* Rework the imports

* More reexports rework

* Add documentation

* Move finalization report to network future

* Move on_block_imported to worker

* get_value/put_value no longer locking

* local_peer_id() no longer locks

* Remove FetchFuture

* Service imports cleanup

* Produce the network state in the network task

* Merge network task and RPC network task

* Move network methods to NetworkWorker

* Remove Arc peers system from network

* add_reserved_peer now goes through the channel

* Remove Mutex around network swarm

* Remove the FnOnce alias traits

* Replace is_offline with num_connected

* Improve style of poll()

* Fix network tests

* Some doc in service module

* Remove macro export

* Minor doc changes

* Remove the synchronized() method of the import queue

* Line width

* Line widths

* Fix import queue tests

* Fix CLI tests