Westend Mock Runtime and Client (#874)

* Copy-Pasta Call code from mock Rococo to mock Westend runtime

* Update Westend client to include signing and call related code

* Add missing part of license header

* Move `account_info_storage_key` to `polkadot-core` crate

bridges/relays/client-rococo/src/lib.rs

@@ -1,3 +1,6 @@
+// Copyright 2019-2021 Parity Technologies (UK) Ltd.
+// This file is part of Parity Bridges Common.
+
 // Parity Bridges Common is free software: you can redistribute it and/or modify
 // it under the terms of the GNU General Public License as published by
 // the Free Software Foundation, either version 3 of the License, or
@@ -22,6 +25,9 @@ use std::time::Duration;
 /// Rococo header id.
 pub type HeaderId = relay_utils::HeaderId<bp_rococo::Hash, bp_rococo::BlockNumber>;
 
+/// Rococo header type used in headers sync.
+pub type SyncHeader = relay_substrate_client::SyncHeader<bp_rococo::Header>;
+
 /// Rococo chain definition
 #[derive(Debug, Clone, Copy)]
 pub struct Rococo;
@@ -111,6 +117,3 @@ impl Default for SigningParams {
 		}
 	}
 }
-
-/// Rococo header type used in headers sync.
-pub type SyncHeader = relay_substrate_client::SyncHeader<bp_rococo::Header>;