simplify configuration of external login providers

Oqtane.Shared/Models/ExternalLoginProvider.cs

@@ -0,0 +1,11 @@
+using System.Collections.Generic;
+
+namespace Oqtane.Models
+{
+    public class ExternalLoginProvider
+    {
+        public string Name { get; set; }
+
+        public Dictionary<string, string> Settings { get; set; }
+    }
+}