Make test-client generic over runtime (#2824)

* Make test-client generic over runtime.

* Make sure genesis storage is constructed correctly.

* Use prelude in tests.

* Add an example of how to use test-client with node/runtime.

* Bump version.

* Rename test-clients.

substrate/core/client/src/light/fetcher.rs

@@ -491,7 +491,7 @@ pub mod tests {
 	use executor::{self, NativeExecutionDispatch};
 	use crate::error::Error as ClientError;
 	use test_client::{
-		self, TestClient, blockchain::HeaderBackend, AccountKeyring,
+		self, ClientExt, blockchain::HeaderBackend, AccountKeyring,
 		runtime::{self, Hash, Block, Header, Extrinsic}
 	};
 	use consensus::BlockOrigin;