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) {

lib/settings/purchase_order_settings.dart

@@ -1,6 +1,7 @@
 
 import "package:flutter/material.dart";
 import "package:flutter_tabler_icons/flutter_tabler_icons.dart";
+import "package:inventree/app_colors.dart";
 
 import "package:inventree/l10.dart";
 import "package:inventree/preferences.dart";
@@ -39,7 +40,10 @@ class _InvenTreePurchaseOrderSettingsState extends State<InvenTreePurchaseOrderS
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-        appBar: AppBar(title: Text(L10().purchaseOrderSettings)),
+        appBar: AppBar(
+          title: Text(L10().purchaseOrderSettings),
+          backgroundColor: COLOR_APP_BAR,
+        ),
         body: Container(
             child: ListView(
                 children: [

lib/settings/sales_order_settings.dart

@@ -3,6 +3,7 @@ import "package:flutter/material.dart";
 import "package:flutter_tabler_icons/flutter_tabler_icons.dart";
 
 import "package:inventree/l10.dart";
+import "package:inventree/app_colors.dart";
 import "package:inventree/preferences.dart";
 
 
@@ -39,7 +40,10 @@ class _InvenTreeSalesOrderSettingsState extends State<InvenTreeSalesOrderSetting
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-        appBar: AppBar(title: Text(L10().salesOrderSettings)),
+        appBar: AppBar(
+          title: Text(L10().salesOrderSettings),
+          backgroundColor: COLOR_APP_BAR,
+        ),
         body: Container(
             child: ListView(
                 children: [

lib/settings/select_server.dart

@@ -266,6 +266,7 @@ class _InvenTreeSelectServerState extends State<InvenTreeSelectServerWidget> {
       key: _loginKey,
       appBar: AppBar(
         title: Text(L10().profileSelect),
+        backgroundColor: COLOR_APP_BAR,
         actions: [
           IconButton(
             icon: Icon(TablerIcons.circle_plus),