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/ApplicationCore/Interfaces/IEmailSender.cs

@@ -0,0 +1,10 @@
+using System.Threading.Tasks;
+
+namespace ApplicationCore.Interfaces
+{
+
+    public interface IEmailSender
+    {
+        Task SendEmailAsync(string email, string subject, string message);
+    }
+}