- Updating ExtensionManager and ThemeService to read zones from the manifest.

- Adding a few essential parts for layers, widgets.

--HG--
branch : dev

src/Orchard.Web/Modules/Orchard.Widgets/Models/LayerZone.cs

@@ -0,0 +1,7 @@
+using System.Collections.Generic;
+
+namespace Orchard.Widgets.Models {
+    public class LayerZone {
+        public IList<WidgetPart> WidgetParts = new List<WidgetPart>();
+    }
+}