Refactored sort system a little

To standardise the handled data format a little better.

app/Entities/Tools/BookSortMapItem.php

@@ -0,0 +1,51 @@
+<?php
+
+namespace BookStack\Entities\Tools;
+
+use BookStack\Entities\Models\BookChild;
+
+class BookSortMapItem
+{
+
+    /**
+     * @var int
+     */
+    public $id;
+
+    /**
+     * @var int
+     */
+    public $sort;
+
+    /**
+     * @var ?int
+     */
+    public $parentChapterId;
+
+    /**
+     * @var string
+     */
+    public $type;
+
+    /**
+     * @var int
+     */
+    public $parentBookId;
+
+    /**
+     * @var ?BookChild
+     */
+    public $model = null;
+
+
+    public function __construct(int $id, int $sort, ?int $parentChapterId, string $type, int $parentBookId)
+    {
+        $this->id = $id;
+        $this->sort = $sort;
+        $this->parentChapterId = $parentChapterId;
+        $this->type = $type;
+        $this->parentBookId = $parentBookId;
+    }
+
+
+}