Unify error enums in substrate and ethereum clients with thiserror (#1094)

* Unify error enums in substrate and ethereum clients with `thiserror`

Related to https://github.com/paritytech/parity-bridges-common/issues/857

* Add license pre-amble

* rustfmt

* Fix spelling

bridges/relays/bin-substrate/src/cli/mod.rs

@@ -257,7 +257,7 @@ pub trait CliChain: relay_substrate_client::Chain {
 	/// Construct message payload to be sent over the bridge.
 	fn encode_message(
 		message: crate::cli::encode_message::MessagePayload,
-	) -> Result<Self::MessagePayload, String>;
+	) -> anyhow::Result<Self::MessagePayload>;
 
 	/// Maximal extrinsic weight (from the runtime).
 	fn max_extrinsic_weight() -> Weight;

bridges/relays/bin-substrate/src/cli/resubmit_transactions.rs

@@ -141,6 +141,7 @@ impl ResubmitTransactions {
 					)
 				})
 				.await
+				.map_err(Into::into)
 		})
 	}
 }