Adds Content, ContentStatus and ContentType implementations U4-922 and U4-923.

Hiding language property untill its fully implemented.
Making set on Parent Id private.
Resolves a naming conflict in DocumentExtensions and DefaultPublishedMediaStore.

src/Umbraco.Web/DefaultPublishedMediaStore.cs

@@ -10,6 +10,7 @@ using Umbraco.Core.Dynamics;
 using Umbraco.Core.Models;
 using umbraco;
 using umbraco.cms.businesslogic;
+using ContentType = umbraco.cms.businesslogic.ContentType;
 
 namespace Umbraco.Web
 {