Add U2f Login Support (#787)

* init u2f

* ux fixes

* Cleanup Manage Controller

* final changes

* remove logs

* remove console log

* fix text for u2f

* Use Is Secure instead of IsHttps

* add some basic u2f tests

* move loaders to before title

* missing commit

* refactor after nicolas wtf moment

BTCPayServer/U2F/Models/U2FAuthenticationViewModel.cs

@@ -0,0 +1,10 @@
+using System.Collections.Generic;
+
+namespace BTCPayServer.Services.U2F.Models
+{
+    public class U2FAuthenticationViewModel
+    {
+        public string StatusMessage { get; set; }
+        public List<U2FDevice> Devices { get; set; }
+    }
+}