Closes #547 Add option to add relationship property attributes

[ArnaudB88]

Resolves #547
Add an option to add attributes on navigation properties in the generated entity classes.

YAML usage:

data:
  entity:
    relationshipAttributes: 'Ignore'

Code generation result:

public partial class Project
{
    #region Generated Relationships
    [Ignore]
    public virtual ICollection<Item> Items { get; set; }
    #endregion
}