Add notifications on missing functionality

flutter/lib/pages/message_view/message_view.dart

@@ -210,7 +210,13 @@ class _MessageViewPageState extends State<MessageViewPage> {
             values: [_prettyPrintPriority(message.priority)],
             mainAction: () => Navi.push(context, () => FilteredMessageViewPage(title: "Priority ${message.priority}", filter: MessageFilter(priority: [message.priority]))),
           ),
-          if (message.senderUserID == userAccUserID) UI.button(text: "Delete Message", onPressed: () {/*TODO*/}, color: Colors.red[900]),
+          if (message.senderUserID == userAccUserID)
+            UI.button(
+                text: "Delete Message",
+                onPressed: () {
+                  Toaster.info("Not Implemented", "... will be implemented in a later version"); // TODO
+                },
+                color: Colors.red[900]),
         ],
       ),
     );