Scanner wedge mode (#437)

* Add code_scan_listener package

* Implement wedge controller widget

* Update barcode settings widget

- Allow user to choose which barcode scanner to use

* Fix typo

* Select barcode scanner widget based on user preference

* Fix rendering issues for wedge controller

* Update release notes

* Add unit test for wedge scanner widget

- Required some tweaks to other code

* Use better library

- https://github.com/fuadreza/flutter_barcode_listener
- Fork of https://github.com/shaxxx/flutter_barcode_listener
- Properly handles key "case" issues (shift, essentially)
- Verified that it works correctly for multiple character types

* Local copy of code, rather than relying on package which is not available on pub.dev

* Fix unit test

lib/app_colors.dart

@@ -6,6 +6,11 @@ const Color COLOR_GRAY_LIGHT = Color.fromRGBO(150, 150, 150, 1);
 // Return an "action" color based on the current theme
 Color get COLOR_ACTION {
 
+  // OneContext might not have context, e.g. in testing
+  if (!OneContext.hasContext) {
+    return Colors.lightBlue;
+  }
+
   BuildContext? context = OneContext().context;
 
   if (context != null) {