Added user authorization (not tested)

FoxTube.Core/Models/User.cs

@@ -0,0 +1,24 @@
+using Google.Apis.Auth.OAuth2;
+using Google.Apis.YouTube.v3.Data;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace FoxTube.Core.Models
+{
+    public class User
+    {
+        public string Name { get; set; }
+        public string Email { get; set; }
+        internal string RefreshToken { get; set; }
+        public UserCredential Credential { get; set; }
+        public Channel Channel { get; set; }
+
+        public User(UserCredential credential)
+        {
+
+        }
+    }
+}