Implement AuthService and ApiClient core logic

Models/FileTransferModels.cs

@@ -0,0 +1,17 @@
+using System.Collections.Generic;
+
+namespace Chtn.CSharp.SDK.Models.Media
+{
+    public class StartNewFileTransferReq
+    {
+        public string UserId { get; set; }
+        public string TargetUserId { get; set; }
+        public List<TransferableFileMetadata> Metadata { get; set; }
+    }
+    public class TransferableFileMetadata
+    {
+        public string FileId { get; set; }
+        public string Name { get; set; }
+        public long Size { get; set; }
+    }
+}