Replace old markdown and remove redundant events (#389)

* Remove redundant messages

* Replaced old markdown with preview.
Added nuget config to add preview feed

* Fix old extensions usage

* Scrollbar margin for the markdown.

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Co-authored-by: Burak Kaan Köse <bkaankose@outlook.com>

Wino.Mail.ViewModels/MailListPageViewModel.cs

@@ -28,7 +28,6 @@ using Wino.Mail.ViewModels.Collections;
 using Wino.Mail.ViewModels.Data;
 using Wino.Mail.ViewModels.Messages;
 using Wino.Messaging.Client.Mails;
-using Wino.Messaging.Client.Shell;
 using Wino.Messaging.Server;
 using Wino.Messaging.UI;
 
@@ -283,8 +282,6 @@ namespace Wino.Mail.ViewModels
 
             if (isMultiSelecting && StatePersistenceService.IsReaderNarrowed)
             {
-                // Don't change the active mail item if the reader is narrowed, but just update the shell.
-                Messenger.Send(new ShellStateUpdated());
                 return;
             }