Custom RPC implementation for node. (#3109)

* Allow RPCs to be customized.

* Implement node-rpc extensions.

* Working on a test.

* Add node-testing crate.

* Fix genesis test config

* Fix nonce lookups.

* Clean up.

* Fix expected block type.

* Make the RPC extension function optional.

* Fix service doc test.

* Bump jsonrpc.

* Bump client version.

* Update Cargo.lock

* Update jsonrpc.

* Fix build.

* Remove unused imports.

* Fix signed extra.

* Post merge clean up.

* Fix tests.

* Patch hashmap-core.

* Fix build.

* Fix build.

* Remove hashmap_core patches.

substrate/core/test-client/src/lib.rs

@@ -67,7 +67,7 @@ impl GenesisInit for () {
 }
 
 /// A builder for creating a test client instance.
-pub struct TestClientBuilder<Executor, Backend, G: GenesisInit = ()> {
+pub struct TestClientBuilder<Executor, Backend, G: GenesisInit> {
 	execution_strategies: ExecutionStrategies,
 	genesis_init: G,
 	child_storage_extension: HashMap<Vec<u8>, Vec<(Vec<u8>, Vec<u8>)>>,
@@ -76,9 +76,10 @@ pub struct TestClientBuilder<Executor, Backend, G: GenesisInit = ()> {
 	keystore: Option<BareCryptoStorePtr>,
 }
 
-impl<Block, Executor> Default for TestClientBuilder<
+impl<Block, Executor, G: GenesisInit> Default for TestClientBuilder<
 	Executor,
 	Backend<Block>,
+	G,
 > where
 	Block: BlockT<Hash=<Blake2Hasher as Hasher>::Out>,
 {