Barcode scanner updates (#562)

* Add BUILDING.md

* Replace scaning library

- Out with qr_code_scanner
- In with flutter_zxing

* Update specs for jdk / kotlin / gradle

- NFI what this all means?

* Refactor barcode scanning widget

* Refactor barcode overlay

* Add handlers

* Update release notes

* Fix AppBar color

* Enhance attachment widget

* remove unused import

* Improved icon

* Select theme from main drawer

lib/barcode/handler.dart

@@ -60,6 +60,7 @@ class BarcodeHandler {
   Future<void> processBarcode(String barcode,
       {String url = "barcode/",
       Map<String, dynamic> extra_data = const {}}) async {
+
     debug("Scanned barcode data: '${barcode}'");
 
     barcode = barcode.trim();