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/settings/app_settings.dart

@@ -174,7 +174,7 @@ class _InvenTreeAppSettingsState extends State<InvenTreeAppSettingsWidget> {
             ListTile(
               title: Text(L10().darkMode),
               subtitle: Text(L10().darkModeEnable),
-              leading: Icon(TablerIcons.moon),
+              leading: Icon(TablerIcons.sun_moon),
               trailing: Switch(
                 value: darkMode,
                 onChanged: (bool value) {