Multi-call RPC (#6195)

* Removing duplicated pending state accessors in miner.

* Merge miner+client call.

* Multicall & multicall RPC.

* Sensible defaults.

* Fix tests.

sync/src/block_sync.rs

@@ -267,7 +267,7 @@ impl BlockDownloader {
 				BlockStatus::Bad => {
 					return Err(BlockDownloaderImportError::Invalid);
 				},
-				BlockStatus::Unknown => {
+				BlockStatus::Unknown | BlockStatus::Pending => {
 					headers.push(hdr.as_raw().to_vec());
 					hashes.push(hash);
 				}