Added IRegistryCore and RegistryCore to OpenSim.Framework.

Added a ApplicationRegistry to OpenSimBase.
Changed LoadRegionsPlugin so it registers itself to that application registry.
Added a event to LoadRegionsPlugin, that is triggered when it creates a new scene ,although maybe this event should actually be in opensimBase incase other plugins are creating regions (like the RemoteAdminPlugin).

OpenSim/Framework/IRegistryCore.cs

@@ -0,0 +1,13 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace OpenSim.Framework
+{
+    public interface IRegistryCore
+    {
+        T Get<T>();
+        void RegisterInterface<T>(T iface);
+        bool TryGet<T>(out T iface);
+    }
+}