Signed extension to refund relayer at the target chain (#1657)

* add utlity pallet to the Millau runtime

* RefundRelayerForMessagesDeliveryFromParachain prototype

* done with RefundRelayerForMessagesDeliveryFromParachain::post_dispatch

* parse calls

* check batch for obsolete headers/messages

* fmt

* shorten generic arg names + add parachain id generic arg

* check lane_id

* impl all state read functions

* fix typos from review

* renamed extension + reference issue from TODO

* tests for pre-dispaytch

* renamed extension source file

* tests for post-dispatch

* abstract fee calculation

* clippy

* actually fix clippy

* Update bin/runtime-common/src/refund_relayer_extension.rs

Co-authored-by: Adrian Catangiu <adrian@parity.io>

* Update bin/runtime-common/src/refund_relayer_extension.rs

Co-authored-by: Adrian Catangiu <adrian@parity.io>

* Update bin/runtime-common/src/refund_relayer_extension.rs

Co-authored-by: Adrian Catangiu <adrian@parity.io>

* Update bin/runtime-common/src/refund_relayer_extension.rs

Co-authored-by: Adrian Catangiu <adrian@parity.io>

Co-authored-by: Adrian Catangiu <adrian@parity.io>

bridges/modules/messages/src/lib.rs

@@ -168,10 +168,10 @@ pub mod pallet {
 	}
 
 	/// Shortcut to messages proof type for Config.
-	type MessagesProofOf<T, I> =
+	pub type MessagesProofOf<T, I> =
 		<<T as Config<I>>::SourceHeaderChain as SourceHeaderChain>::MessagesProof;
 	/// Shortcut to messages delivery proof type for Config.
-	type MessagesDeliveryProofOf<T, I> =
+	pub type MessagesDeliveryProofOf<T, I> =
 		<<T as Config<I>>::TargetHeaderChain as TargetHeaderChain<
 			<T as Config<I>>::OutboundPayload,
 			<T as frame_system::Config>::AccountId,
@@ -631,6 +631,11 @@ pub mod pallet {
 				dispatch_weight: T::MessageDispatch::dispatch_weight(&mut dispatch_message),
 			}
 		}
+
+		/// Return inbound lane data.
+		pub fn inbound_lane_data(lane: LaneId) -> InboundLaneData<T::InboundRelayer> {
+			InboundLanes::<T, I>::get(lane).0
+		}
 	}
 }