Added support for default sorting. Commodity are sorted by name by default.

commodity/commodityservice.cpp

@@ -40,3 +40,8 @@ ISeller *CommodityService::seller()
 {
     return NULL;
 }
+
+QString CommodityService::defaultSort()
+{
+    return "name";
+}

commodity/commodityservice.h

@@ -16,6 +16,7 @@ public:
     void addedToVoucher(int itemId, int countAdded) override;
     virtual ShopItemPtr shopItem(int itemId) override;
     ISeller *seller() override;
+    QString defaultSort() override;
 };
 
 #endif // COMMODITYSERVICE_H