Implemented concrete powder

this is a little buggy with water updating due to a hack for liquids to fix a CPU leak (210bdc2436), but everything works fine when a block nearby gets updated.

src/pocketmine/block/ConcretePowder.php

@@ -0,0 +1,74 @@
+<?php
+
+/*
+ *
+ *  ____            _        _   __  __ _                  __  __ ____
+ * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
+ * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
+ * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
+ * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * @author PocketMine Team
+ * @link http://www.pocketmine.net/
+ *
+ *
+*/
+
+declare(strict_types=1);
+
+namespace pocketmine\block;
+
+use pocketmine\block\utils\ColorBlockMetaHelper;
+use pocketmine\level\Level;
+use pocketmine\level\Position;
+
+class ConcretePowder extends Fallable{
+
+	protected $id = self::CONCRETE_POWDER;
+
+	public function __construct(int $meta = 0){
+		$this->meta = $meta;
+	}
+
+	public function getName() : string{
+		return ColorBlockMetaHelper::getColorFromMeta($this->meta) . " Concrete Powder";
+	}
+
+	public function getHardness() : float{
+		return 0.5;
+	}
+
+	public function onUpdate(int $type){
+		if($type === Level::BLOCK_UPDATE_NORMAL and ($block = $this->checkAdjacentWater()) !== null){
+			$this->level->setBlock($this, $block);
+			return $type;
+		}
+
+		return parent::onUpdate($type);
+	}
+
+	/**
+	 * @return null|Block
+	 */
+	public function tickFalling() : ?Block{
+		return $this->checkAdjacentWater();
+	}
+
+	/**
+	 * @return null|Block
+	 */
+	private function checkAdjacentWater(){
+		for($i = 1; $i < 6; ++$i){ //Do not check underneath
+			if($this->getSide($i) instanceof Water){
+				return Block::get(Block::CONCRETE, $this->meta);
+			}
+		}
+
+		return null;
+	}
+}