updated project linter-rules and enforced them

lib/view/pages/more/message/message.dart

@@ -27,7 +27,7 @@ class _MessageState extends State<Message> {
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
-        title: const Text("Marianum Message"),
+        title: const Text('Marianum Message'),
       ),
       body: Consumer<MessageProps>(builder: (context, value, child) {
         if(value.primaryLoading()) return const LoadingSpinner();
@@ -43,7 +43,7 @@ class _MessageState extends State<Message> {
                     children: [Icon(Icons.newspaper)],
                   ),
                   title: Text(message.name, overflow: TextOverflow.ellipsis),
-                  subtitle: Text("vom ${message.date}"),
+                  subtitle: Text('vom ${message.date}'),
                   trailing: const Icon(Icons.arrow_right),
                   onTap: () {
                     Navigator.push(context, MaterialPageRoute(builder: (context) => MessageView(basePath: value.getMessagesResponse.base, message: message)));

lib/view/pages/more/message/messageView.dart

@@ -29,12 +29,12 @@ class _MessageViewState extends State<MessageView> {
           Navigator.of(context).pop();
           showDialog(context: context, builder: (context) {
             return AlertDialog(
-              title: const Text("Fehler beim öffnen"),
+              title: const Text('Fehler beim öffnen'),
               content: Text("Dokument '${widget.message.name}' konnte nicht geladen werden:\n${e.description}"),
               actions: [
                 TextButton(onPressed: () {
                   Navigator.of(context).pop();
-                }, child: const Text("Ok"))
+                }, child: const Text('Ok'))
               ],
             );
           });
@@ -43,9 +43,9 @@ class _MessageViewState extends State<MessageView> {
           showDialog(
             context: context,
             builder: (context) => ConfirmDialog(
-              title: "Link öffnen",
-              content: "Möchtest du den folgenden Link öffnen?\n${e.uri}",
-              confirmButton: "Öffnen",
+              title: 'Link öffnen',
+              content: 'Möchtest du den folgenden Link öffnen?\n${e.uri}',
+              confirmButton: 'Öffnen',
               onConfirm: () => launchUrl(Uri.parse(e.uri), mode: LaunchMode.externalApplication),
             ),
           );