Multi-call RPC (#6195)

* Removing duplicated pending state accessors in miner.

* Merge miner+client call.

* Multicall & multicall RPC.

* Sensible defaults.

* Fix tests.

ethcore/src/engines/tendermint/mod.rs

@@ -1050,7 +1050,7 @@ mod tests {
 		client.miner().import_own_transaction(client.as_ref(), transaction.into()).unwrap();
 
 		// Propose
-		let proposal = Some(client.miner().pending_block().unwrap().header.bare_hash());
+		let proposal = Some(client.miner().pending_block(0).unwrap().header.bare_hash());
 		// Propose timeout
 		engine.step();