Clean up Flutter warnings

lib/main_app.dart

@@ -308,7 +308,7 @@ class InvoiceNinjaAppState extends State<InvoiceNinjaApp> {
           );
 
           final outlinedButtonTheme = OutlinedButton.styleFrom(
-            primary:
+            foregroundColor:
                 state.prefState.enableDarkMode ? Colors.white : Colors.black87,
           );
 

lib/ui/app/buttons/app_text_button.dart

@@ -39,7 +39,7 @@ class AppTextButton extends StatelessWidget {
     }
 
     final ButtonStyle flatButtonStyle =
-        TextButton.styleFrom(primary: primaryColor);
+        TextButton.styleFrom(foregroundColor: primaryColor);
 
     return TextButton(
       style: flatButtonStyle,

lib/ui/app/buttons/elevated_button.dart

@@ -24,7 +24,7 @@ class AppButton extends StatelessWidget {
   Widget build(BuildContext context) {
     final button = ElevatedButton(
       style: ElevatedButton.styleFrom(
-        primary: color ?? Theme.of(context).colorScheme.secondary,
+        foregroundColor: color ?? Theme.of(context).colorScheme.secondary,
         padding: EdgeInsets.symmetric(vertical: 14, horizontal: 14),
         shape: RoundedRectangleBorder(
             borderRadius: BorderRadius.circular(kBorderRadius)),

lib/ui/design/edit/design_edit.dart

@@ -1,6 +1,5 @@
 // Dart imports:
 import 'dart:convert';
-import 'dart:typed_data';
 import 'dart:ui';
 
 // Flutter imports:

lib/ui/settings/settings_screen_vm.dart

@@ -9,7 +9,6 @@ import 'package:redux/redux.dart';
 // Project imports:
 import 'package:invoiceninja_flutter/redux/app/app_state.dart';
 import 'package:invoiceninja_flutter/ui/settings/settings_screen.dart';
-import 'settings_screen.dart';
 
 class SettingsScreenBuilder extends StatelessWidget {
   const SettingsScreenBuilder({Key key}) : super(key: key);