Added darkmode for chat view

lib/data/appTheme.dart

@@ -22,6 +22,10 @@ class AppTheme extends ChangeNotifier {
 
     }
   }
+
+  static bool isDarkMode(BuildContext context) {
+    return Theme.of(context).brightness == Brightness.dark;
+  }
 }
 
 class ThemeModeDisplay {