Snapshot sync part 2 (#2098)

* Split block downloader into a module

* Snapshot sync progress

* Warp sync CLI option

* Increased snapshot chunk and ping timeouts

* Fixed an issue with delayed writes

* Updated bootnodes

* Don't run pending IO tasks on shutdown

* Optional first_block; removed insert_snapshot_block

* Fixing expect calls

* Fixed stalled sync

* style and docs

* Update block_sync.rs

[ci:skip]

util/io/src/worker.rs

@@ -101,11 +101,11 @@ impl Worker {
 				let _ = wait.wait(lock);
 			}
 
-			if deleting.load(AtomicOrdering::Acquire) {
-				return;
-			}
-			while let chase_lev::Steal::Data(work) = stealer.steal() {
-				Worker::do_work(work, channel.clone());
+			while !deleting.load(AtomicOrdering::Acquire) {
+				match stealer.steal() {
+					chase_lev::Steal::Data(work) => Worker::do_work(work, channel.clone()),
+					_ => break,
+				}
 			}
 		}
 	}