Adding 2FA Authenticator Support (#66)

* Adding support for 2fa, more auth options

* WIP getting auth stuff working

* Added Manage views. 2FA working now for MVC app.

* Switching to using a controller for no-UI logout scenario

* Adding Razor Pages impl of 2FA auth stuff. Works.

src/Web/ViewModels/Manage/ExternalLoginsViewModel.cs

@@ -0,0 +1,14 @@
+using Microsoft.AspNetCore.Authentication;
+using Microsoft.AspNetCore.Identity;
+using System.Collections.Generic;
+
+namespace Microsoft.eShopWeb.ViewModels.Manage
+{
+    public class ExternalLoginsViewModel
+    {
+        public IList<UserLoginInfo> CurrentLogins { get; set; }
+        public IList<AuthenticationScheme> OtherLogins { get; set; }
+        public bool ShowRemoveButton { get; set; }
+        public string StatusMessage { get; set; }
+    }
+}