Refactoring IModule and ITheme related services

Changing component layering to allow more efficient dependencies
Marking several interfaces and services obsolete to produce warnings
Changing ITheme to FeatureDescriptor as a first step

--HG--
branch : perf
extra : rebase_source : 905b69eb1cc6ed05750908e41a2d0846dde22001

src/Orchard.Web/Global.asax.cs

@@ -37,6 +37,7 @@ namespace Orchard.Web {
 
         protected void Application_EndRequest() {
             _host.EndRequest();
+            GC.Collect();
         }
 
         static void MvcSingletons(ContainerBuilder builder) {