Implement auto-update via Onova

DiscordChatExporter.Gui/Messages/ShowNotificationMessage.cs

@@ -0,0 +1,25 @@
+using System;
+
+namespace DiscordChatExporter.Gui.Messages
+{
+    public class ShowNotificationMessage
+    {
+        public string Message { get; }
+
+        public string CallbackCaption { get; }
+
+        public Action Callback { get; }
+
+        public ShowNotificationMessage(string message)
+        {
+            Message = message;
+        }
+
+        public ShowNotificationMessage(string message, string callbackCaption, Action callback)
+            : this(message)
+        {
+            CallbackCaption = callbackCaption;
+            Callback = callback;
+        }
+    }
+}