Refactored the GridServer into a GridDBService and a set of "modules".

Currently they aren't plugin modules as the support for dynamically loading them isn't complete.

OpenSim/Grid/GridServer/IGridMessagingModule.cs

@@ -0,0 +1,11 @@
+using System;
+using System.Collections.Generic;
+using OpenSim.Framework.Servers;
+
+namespace OpenSim.Grid.GridServer
+{
+    public interface IGridMessagingModule
+    {
+        List<MessageServerInfo> MessageServers { get; }
+    }
+}