Embedded images replaced with cid linked resources. (#313)

* Added logic to replace embedded images with linked resources

* Added alt text for images and replaced NewtonSoft with Text.Json

* Fix draft mime preparation

* Fix crashes for signatures without images.

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

Wino.Mail/Activation/FileActivationHandler.cs

@@ -2,6 +2,7 @@
 using System.IO;
 using System.Linq;
 using System.Threading.Tasks;
+using Microsoft.Toolkit.Uwp.Helpers;
 using Windows.ApplicationModel.Activation;
 using Windows.Storage;
 using Windows.UI.Xaml;
@@ -9,7 +10,6 @@ using Windows.UI.Xaml.Controls;
 using Windows.UI.Xaml.Media.Animation;
 using Wino.Core.Domain.Interfaces;
 using Wino.Core.Services;
-using Wino.Helpers;
 using Wino.Views;
 
 namespace Wino.Activation