Added some fields to new packets

gave up on EventPacket because it's a mess, and StructureBlockUpdate is a job all by itself

src/pocketmine/network/mcpe/protocol/AddBehaviorTreePacket.php

@@ -30,12 +30,15 @@ use pocketmine\network\mcpe\NetworkSession;
 class AddBehaviorTreePacket extends DataPacket{
 	const NETWORK_ID = ProtocolInfo::ADD_BEHAVIOR_TREE_PACKET;
 
+	/** @var string */
+	public $unknownString1;
+
 	public function decodePayload(){
-		//TODO
+		$this->unknownString1 = $this->getString();
 	}
 
 	public function encodePayload(){
-		//TODO
+		$this->putString($this->unknownString1);
 	}
 
 	public function handle(NetworkSession $session) : bool{