Ignore members with [NotMapped] in support of IUser<int> Indentity 2.x

I need to add [NotMapped] attribute to support IUser<int> in Identity 2.x

If you have a poco, say, MyAppUser, with UserId (int) as [Key], then you still need an Id field to support the IUser interface. You can't store this member in DB as the column doesn't exist

[NotMapped]
public int Id
{
    get { return UserId; }
}