Refactoring entities with Users to only add Id to minimize the object graph.

Moved getting an IProfile to an extension method, as its not commonly used.
Removing dependencies in ContentService, so the Services and context can be moved to Core proj.
Implementing Template repository to use both filesystem and db.

src/Umbraco.Core/Models/IContent.cs

@@ -35,9 +35,9 @@ namespace Umbraco.Core.Models
         DateTime? ExpireDate { get; set; }
 
         /// <summary>
-        /// Profile of the user who wrote the Content
+        /// Id of the user who wrote/updated the Content
         /// </summary>
-        IProfile Writer { get; set; }
+        int WriterId { get; set; }
 
         /// <summary>
         /// Gets the ContentType used by this content object