Server termination and refactoring message dialogs.

Wino.Messages/Server/TerminateServerRequested.cs

@@ -0,0 +1,9 @@
+using Wino.Core.Domain.Interfaces;
+
+namespace Wino.Messaging.Server
+{
+    /// <summary>
+    /// This message is sent to server to kill itself when UWP app is terminating.
+    /// </summary>
+    public record TerminateServerRequested : IClientMessage;
+}