Add prettier config file + recommended extension

WARNING: Really sorry, I tried everything I can but for some reasons, I cannot make a merge request with only the 2 files I commited !! I would be happy to learn how to do it properly ...

The only changes are the last 2 files .prettierrc and .vscode/extensions.json

lib/ui/screens/fifth_screen.dart

@@ -105,6 +105,10 @@ class _FifthScreenState extends State<FifthScreen> {
                             value: Locale('en'),
                             child: Text('English'),
                           ),
+                          DropdownMenuItem<Locale>(
+                            value: Locale('eo'),
+                            child: Text('Esperanto'),
+                          ),
                           DropdownMenuItem<Locale>(
                             value: Locale('es'),
                             child: Text('Español'),