Added ExternalNotificationProviderBase based on IndexProviderBase.

NzbDrone.Core/Model/ExternalNotificationType.cs

@@ -0,0 +1,14 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace NzbDrone.Core.Model
+{
+    public enum ExternalNotificationType
+    {
+        Grab = 0,
+        Download = 1,
+        Rename = 2
+    }
+}