Server Roles: definitions of server roles and attributes
    
    This patch introduces classes which define the properties of server roles and
    attributes and their relationship to LDAP attributes representing the
    role/attribute.
    
    A brief documentation about defining and using roles is given at the beginning
    of the module.
    
    http://www.freeipa.org/page/V4/Server_Roles
    https://fedorahosted.org/freeipa/ticket/5181
    
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>
    Reviewed-By: Martin Basti <mbasti@redhat.com>
    Reviewed-By: Pavel Vomacka <pvomacka@redhat.com>