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

test/wedge_scanner_test.dart

@@ -0,0 +1,32 @@
+
+
+import "package:flutter/material.dart";
+import "package:flutter/services.dart";
+import "package:flutter_test/flutter_test.dart";
+import "package:inventree/barcode/barcode.dart";
+import "package:inventree/barcode/wedge_controller.dart";
+import "package:inventree/helpers.dart";
+
+
+void main() {
+  testWidgets("Wedge Scanner Test", (tester) async {
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: WedgeBarcodeController(BarcodeScanHandler())
+      )
+    );
+
+    // Generate some keyboard data
+    await simulateKeyDownEvent(LogicalKeyboardKey.keyA);
+    await simulateKeyDownEvent(LogicalKeyboardKey.keyB);
+    await simulateKeyDownEvent(LogicalKeyboardKey.keyC);
+    await simulateKeyDownEvent(LogicalKeyboardKey.enter);
+
+    // Check debug output
+    debugContains("scanned: abc");
+    debugContains("No match for barcode");
+    debugContains("Server Error");
+
+  });
+}