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.

---------

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

Wino.Core/Http/MicrosoftJsonContractResolver.cs

@@ -1,36 +0,0 @@
-using Newtonsoft.Json;
-using Newtonsoft.Json.Serialization;
-using System;
-using System.Collections.Generic;
-using System.Reflection;
-using System.Text;
-
-namespace Wino.Core.Http
-{
-
-    /// <summary>
-    /// We need to generate HttpRequestMessage for batch requests, and sometimes we need to
-    /// serialize content as json. However, some of the fields like 'ODataType' must be ignored
-    /// in order PATCH requests to succeed. Therefore Microsoft account synchronizer uses
-    /// special JsonSerializerSettings for ignoring some of the properties.
-    /// </summary>
-    public class MicrosoftJsonContractResolver : DefaultContractResolver
-    {
-        private readonly HashSet<string> ignoreProps = new HashSet<string>()
-        {
-            "ODataType"
-        };
-
-        protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
-        {
-            JsonProperty property = base.CreateProperty(member, memberSerialization);
-
-            if (ignoreProps.Contains(property.PropertyName))
-            {
-                property.ShouldSerialize = _ => false;
-            }
-
-            return property;
-        }
-    }
-}