Support no primary key entity code generation

[gdlcf88]

The entity code:

public class ResourceItemContent : FullAuditedEntity
{
        public virtual Guid ResourceItemId { get; protected set; }

        [NotNull]
        public virtual string Content { get; protected set; }

        public override object[] GetKeys()
        {
            return new object[] {ResourceItemId};
        }
}

Problem 1: Wrong base class.

Problem 2: Need to set b.HasKey(), or the migration will not work well. But how do we know what the keys are? (Only GetKeys() in entity class know this information)