added throwable eggs and refactor some projectile logic

close #1473

src/pocketmine/item/Egg.php

@@ -23,12 +23,21 @@ declare(strict_types=1);
 
 namespace pocketmine\item;
 
-class Egg extends Item{
+class Egg extends ProjectileItem{
 	public function __construct(int $meta = 0){
 		parent::__construct(self::EGG, $meta, "Egg");
 	}
 
-	//TODO
+	public function getMaxStackSize() : int{
+		return 16;
+	}
 
+	public function getProjectileEntityType() : string{
+		return "Egg";
+	}
+
+	public function getThrowForce() : float{
+		return 1.5;
+	}
 }