Initial version of DummyOrdered pallet (#299)

* initial commit of DummyOrdered (aka message-lane) pallet

* API for relay

* cargo fmt --all

* some clippy + no_std

* more clippy + no_std

* inbound lane tests

* outbound lane tests

* cargo fmt --all

* prune old messages whenever outbound lane is updated

* do not care about MessageNonce overflow

* cargo fmt --all

* update crate docs

* MaxHeadersToPruneAtOnce -> MaxMessagesToPruneAtOnce

* MessageAction -> MessageResult

* cargo fmt --all

* fire MessageAccepted + MessagesDelivered

* confirm message processing

* cargo fmt --all

* clippy

* cargo fmt again

* Update modules/message-lane/src/lib.rs

Co-authored-by: Hernando Castano <[email protected]>

* Update modules/message-lane/src/lib.rs

Co-authored-by: Hernando Castano <[email protected]>

* use crate::*

* cargo fmt --all

* Storage -> S

* Update modules/message-lane/src/outbound_lane.rs

Co-authored-by: Hernando Castano <[email protected]>

* add method doc

* Update modules/message-lane/src/inbound_lane.rs

Co-authored-by: Hernando Castano <[email protected]>

* added detailed module docs

* Update modules/message-lane/src/lib.rs

Co-authored-by: Tomasz Drwięga <[email protected]>

* updated OnMessageReceived docs

* prune only when new message is sent

* removed #![warn(missing_docs)]

* fixed merge with overlapped PR

Co-authored-by: Hernando Castano <[email protected]>
Co-authored-by: Tomasz Drwięga <[email protected]>