Provider testing improvements

New: Test button for indexers in UI

Fixed: Testing download clients shows error messages in UI
Fixed: Testing notifications shows error messages in UI

src/NzbDrone.Core/Notifications/NotificationDefinition.cs

@@ -8,5 +8,13 @@ namespace NzbDrone.Core.Notifications
         public Boolean OnGrab { get; set; }
         public Boolean OnDownload { get; set; }
         public Boolean OnUpgrade { get; set; }
+
+        public override Boolean Enable
+        {
+            get
+            {
+                return OnGrab || OnDownload || OnUpgrade;
+            }
+        }
     }
-}
+}