Send messages using xcm pallet (#1518)

* send messages using xcm pallet

* XcmBridge && XcmBridgeAdapter + (untested) config in RialtoParachain

* impl encode_send_xcm for the rest

* remove duplicate code

* some fixes

* cleanup

* some more tests

* cleanup

* cleanup

* send Rialto -> Millau messages using bridge-messages pallet

* fmt

* some clippy fixes

* more clippy

bridges/bin/millau/runtime/src/rialto_parachain_messages.rs

@@ -38,6 +38,8 @@ use scale_info::TypeInfo;
 use sp_runtime::{traits::Saturating, FixedPointNumber, FixedU128};
 use sp_std::convert::TryFrom;
 
+/// Default lane that is used to send messages to Rialto parachain.
+pub const DEFAULT_XCM_LANE_TO_RIALTO_PARACHAIN: LaneId = [0, 0, 0, 0];
 /// Weight of 2 XCM instructions is for simple `Trap(42)` program, coming through bridge
 /// (it is prepended with `UniversalOrigin` instruction). It is used just for simplest manual
 /// tests, confirming that we don't break encoding somewhere between.
@@ -138,7 +140,7 @@ impl messages::ThisChainWithMessages for Millau {
 	>;
 
 	fn is_message_accepted(_send_origin: &Self::Origin, lane: &LaneId) -> bool {
-		*lane == [0, 0, 0, 0] || *lane == [0, 0, 0, 1]
+		*lane == DEFAULT_XCM_LANE_TO_RIALTO_PARACHAIN || *lane == [0, 0, 0, 1]
 	}
 
 	fn maximal_pending_messages_at_outbound_lane() -> MessageNonce {