Roughing in extensibility model for content type definition editor

IEventHandler method invocation will aggregate return values of type IEnumerable<T>
Added IContentDefinitionEditorEvents and ContentDefinitionEditorEventsBase to framework assembly
ContentTypes editor fires events to build and apply additional type and typepart TemplateViewModel classes
As an example, added some content type settings to devtools "ShowDebugLinks"
In content type definition builder moved DisplayedAs(name) into it's own method
Added Html.RenderTemplates helper to execute renderpartial with prefix directly to bypass (for some cases) Html.EditorXxx, Html.DisplayXxx

--HG--
branch : dev

src/Orchard.Tests.Modules/Settings/Blueprint/ShellDescriptorManagerTests.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 using Autofac;
@@ -28,9 +29,10 @@ namespace Orchard.Tests.Modules.Settings.Blueprint {
             public void Notify_Obsolete(string messageName, IDictionary<string, string> eventData) {
             }
 
-            public void Notify(string messageName, Dictionary<string, object> eventData) {                
+            public IEnumerable Notify(string messageName, Dictionary<string, object> eventData) {                
                 LastMessageName = messageName;
                 LastEventData = eventData;
+                return new object[0];
             }
         }