Ticket 59 - lib389 support for index management.
    
    Bug Description:  To allow tests and dsconf to manage indexes we
    need the supporting objectClasses in place.
    
    Fix Description:  This adds the Indexes
    and Index types, as well as a linking method from a backend to get
    it's related Indexes.
    
    https://pagure.io/lib389/issue/59
    
    Author: wibrown
    
    Review by: ilias95, spichugi (Thanks!)