Added more information into exception in UF:V:login
 - exception now carry important attributes
Merge pull request #258 from papperwing/attributeHolders

- Added more information into exceptions in UF:V:login.
- Prefer throwing WrongAttributeValueException instead of WrongReferenceAttributeValueException
  since in module, we can tell if:
  - facility's namespace is empty (login can't be determined) or
  - user doesn't have login in facility's namespace (null or non-unique). 
 Other cases are handled by standard exceptions (Consistency, AttributeNotExists etc.).