Validation of properties implemented as interfaces

Description

1. Add interface:

   public interface INewsPage

   {

   PageListBlock NewsList { get; set; }

   }

2. Add the property PageListBlock on a page but do not mark it as virtual.

   public class NewsPage : StandardPage, INewsPage

   {

   [Display(

   GroupName = SystemTabNames.Content,

   Order = 305)]

   public PageListBlock NewsList { get; set; }

Expected: An exception that "virtual" is missing.
Actual: Looking at news page, the news list is empty.

Breaking changes note
Validation of content type properties has been changed so properties are checked that PropertyInfo.IsFinal is false. See https://msdn.microsoft.com/en-us/library/system.reflection.methodbase.isfinal(v=vs.110).aspx.
If a property was not supposed to be a content type property (persisted in CMS database) but now throws a validation exception, decorate the property with the [Ignore] attribute.