Created indexing/search default implementation with Lucene

IIndexManager to handle the available IIndexProvider instances
ISearchBuilder created from the used IIndexProvider to create search queries
Indexing background task records
Background service to execute indexing tasks
Unit tests for indexing and searching

--HG--
branch : dev

src/Orchard.Web/Modules/Orchard.Setup/Services/SetupService.cs

@@ -60,6 +60,7 @@ namespace Orchard.Setup.Services {
                     "HomePage",
                     "Navigation",
                     "Scheduling",
+                    "Indexing",
                     "Settings",
                     "XmlRpc",
                     "Orchard.Users",