Xcm in Rialto<>Millau bridge (#1379)

* add XCM pallet to Millau runtime

* some progress

* messages are delivered (no fee)

* temp

* flush

* flush

* some progress

* progress

* Trap(42) is dispatched successfully

* fix spelling

* no more manual sending

* parametrize weight credit for tests

* actually charge fees

* enable send-using-messages-pallet to keep our test deployments alive + send valid XCM sometimes

* fix benchmarks build

* fix tests

bridges/bin/rialto/node/src/chain_spec.rs

@@ -290,6 +290,7 @@ fn testnet_genesis(
 			owner: Some(get_account_id_from_seed::<sr25519::Public>("MillauMessagesOwner")),
 			..Default::default()
 		},
+		xcm_pallet: Default::default(),
 	}
 }