Adding core Containers module

Container part used for content types that group child items together
Containable part provides UI to select which item is ContainerId

--HG--
branch : dev

src/Orchard.Web/Core/Containers/Drivers/ContainablePartDriver.cs

@@ -0,0 +1,7 @@
+using Orchard.ContentManagement.Drivers;
+using Orchard.Core.Containers.Models;
+
+namespace Orchard.Core.Containers.Drivers {
+    public class ContainablePartDriver : ContentPartDriver<ContainablePart> {
+    }
+}