New barcode actions (#218)

* Bump release notes

* Adds method for linking custom barcodes

* Custom getter method for determining if an item has barcode data

* Add method to check if the API supports "modern" barcodes

* Refactor custom barcode implementation for StockItem

- Needs testing

* Unit testing for linking and unlinking barcodes

* Fixes

* Refactor code for "custom barcode action" tile

* Add custom barcode action to StockLocation

* Add extra debug to debug the debugging

* Unit test fix

* Change scope I guess?

* remove handler test

lib/inventree/stock.dart

@@ -276,8 +276,6 @@ class InvenTreeStockItem extends InvenTreeModel {
     });
   }
 
-  String get uid => (jsondata["uid"] ?? "") as String;
-
   int get status => (jsondata["status"] ?? -1) as int;
 
   String get packaging => (jsondata["packaging"] ?? "") as String;