Allowing modules to add interceptors to registered components

Removes reference to Autofac contrib dynamicproxy assembly
Shell factories enable dynamic proxy as dependencies are registered
CurrentUser and CurrentSite interceptors updated for new api
Castle.DynamicProxy2 v2.1 is used to avoid rebuilding nhib binaries

--HG--
branch : dev

src/Orchard.Tests.Modules/Setup/SetupControllerTests.cs

@@ -5,8 +5,8 @@ using System.Web.Routing;
 using Autofac;
 using NUnit.Framework;
 using Orchard.Environment;
+using Orchard.Environment.AutofacUtil;
 using Orchard.Environment.Configuration;
-using Orchard.Environment.ShellBuilders;
 using Orchard.Setup.Controllers;
 using Orchard.Setup.ViewModels;
 using Orchard.UI.Notify;