Asynchronous RPC support (#2017)

* Async RPC

* Limiting number of transactions in queue

* Fixing tests

* Bumping serde and jsonrpc-core

* serde updated to 0.8

* fixed failing tests

* Bumping ipc server

* Fixing API for endpoints

* Experimenting with tests without --release mode

json/src/blockchain/blockchain.rs

@@ -178,5 +178,5 @@ mod tests {
 		}"#;
 		let _deserialized: BlockChain = serde_json::from_str(s).unwrap();
 		// TODO: validate all fields
-	//}
+	}
 }