Notifications can be tested

Notification ImplementationType was added for showing in UI (Humanized/Title cased of Implementation)

NzbDrone.Core/Notifications/Plex/TestPlexServerCommand.cs

@@ -0,0 +1,10 @@
+using NzbDrone.Common.Messaging;
+
+namespace NzbDrone.Core.Notifications.Plex
+{
+    public class TestPlexServerCommand : ICommand
+    {
+        public string Host { get; set; }
+        public int Port { get; set; }
+    }
+}