Moving interfaces for services to Umbraco.Core.

Adding xml extensions for Content to generate xml for the xml cache.
Adding test for xml generation.

src/Umbraco.Core/ApplicationContext.cs

@@ -1,14 +1,9 @@
 using System;
-using System.Collections;
 using System.Configuration;
-using System.Data;
-using System.Diagnostics;
-using System.Linq;
 using System.Web;
 using System.Web.Caching;
 using Umbraco.Core.Configuration;
 using Umbraco.Core.Logging;
-using Umbraco.Core.Models;
 
 
 namespace Umbraco.Core
@@ -138,5 +133,13 @@ namespace Umbraco.Core
             if (this.IsReady)
                 throw new Exception("ApplicationContext has already been initialized.");
         }
+
+        /// <summary>
+        /// Gets the current DatabaseContext
+        /// </summary>
+	    public DatabaseContext DatabaseContext
+	    {
+	        get { return DatabaseContext.Current; }
+	    }
     }
 }