Polkadot service (#82)

* Block import notifications

* Build fix

* Consensus messages supported in the networking

* Started consensus service

* BFT service

* Transaction propagation

* Polkadot service

* CLI integration

* Build fix

* Added signatures validation

* Removed executor argument

* Refactored steam loops; Queue size increased

* Limit queue size

* Fixed doc comment

* Fixed wasm build

* Fixed wasm build

* Check id properly

substrate/polkadot/consensus/src/error.rs

@@ -48,6 +48,10 @@ error_chain! {
 				::MAX_TRANSACTIONS_SIZE, ::MAX_TRANSACTIONS_SIZE.saturating_sub(*size)
 			),
 		}
+		Executor(e: ::futures::future::ExecuteErrorKind) {
+			description("Unable to dispatch agreement future"),
+			display("Unable to dispatch agreement future: {:?}", e),
+		}
 	}
 }