Refactored entity metadata handling into its own class, with type-safe methods (#1876)

This includes several other changes, including:
- SLOT data properties now accept items directly
- POS data properties now accept floored Vector3s (in future this will be block positions) or null for 0,0,0
- VECTOR3F data properties now accept Vector3s or null for 0,0,0

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

@@ -29,7 +29,6 @@ use pocketmine\network\mcpe\NetworkBinaryStream;
 use pocketmine\network\mcpe\NetworkSession;
 use pocketmine\utils\Utils;
 
-
 abstract class DataPacket extends NetworkBinaryStream{
 
 	public const NETWORK_ID = 0;