Add an amoled black theme

lib/main.dart

@@ -263,6 +263,14 @@ class _ObtainiumState extends State<Obtainium> {
         darkColorScheme = ColorScheme.fromSeed(
             seedColor: defaultThemeColour, brightness: Brightness.dark);
       }
+
+      // set the background and surface colors to pure black in the amoled theme
+      if (settingsProvider.useBlackTheme) {
+        darkColorScheme = darkColorScheme
+            .copyWith(background: Colors.black, surface: Colors.black)
+            .harmonized();
+      }
+
       return MaterialApp(
           title: 'Obtainium',
           localizationsDelegates: context.localizationDelegates,

lib/pages/settings.dart

@@ -224,6 +224,17 @@ class _SettingsPageState extends State<SettingsPage> {
                             ),
                             themeDropdown,
                             height16,
+                            Row(
+                              mainAxisAlignment: MainAxisAlignment.spaceBetween,
+                              children: [
+                                Text(tr('useBlackTheme')),
+                                Switch(
+                                    value: settingsProvider.useBlackTheme,
+                                    onChanged: (value) {
+                                      settingsProvider.useBlackTheme = value;
+                                    })
+                              ],
+                            ),
                             colourDropdown,
                             height16,
                             Row(

lib/providers/settings_provider.dart

@@ -64,6 +64,15 @@ class SettingsProvider with ChangeNotifier {
     notifyListeners();
   }
 
+  bool get useBlackTheme {
+    return prefs?.getBool('useBlackTheme') ?? false;
+  }
+
+  set useBlackTheme(bool useBlackTheme) {
+    prefs?.setBool('useBlackTheme', useBlackTheme);
+    notifyListeners();
+  }
+
   int get updateInterval {
     var min = prefs?.getInt('updateInterval') ?? 360;
     if (!updateIntervals.contains(min)) {