Point where basic infoset-based storage of fields is working

Moved some namespaces to reorganize some parts of code
Created a field storage api and default implementation
Added InfosetPart that's always welded as mechanism to reach versioned and non-versioned ad-hoc data

--HG--
branch : dev

src/Orchard.Web/Core/Routable/Drivers/RoutableDriver.cs

@@ -59,7 +59,7 @@ namespace Orchard.Core.Routable.Drivers {
 
             // TEMP: path format patterns replaces this logic
             var path = part.Record.Path;
-            if (path.EndsWith(part.Slug)) {
+            if (path != null && path.EndsWith(part.Slug)) {
                 model.DisplayLeadingPath = path.Substring(0, path.Length - part.Slug.Length);
             }