LDAP: Wizard cannot determine Base DN in some cases, fixes #6670

- disables LDAP referals in Wizard, main fix
- enables Base DN field for editing in Wizard, when Base DN cannot be determined automatically, side fix
- improves performance in Wizard when detecting user attributes and testing base dn (found during debugging)
- also rephrases a log message, resolves #7023 

fixes #6670

please review @PVince81 @ringmaster @DeepDiver1975 or others