Fix bug preventing PHPCR property names being used from mapping

- PHPCR property names mapped by "property" were not being used by many
  of the reference logics in the UOW
- Fixed now to use the "property" mapping instead of the name of the
  mapped classes property.
Merge pull request #299 from dantleech/fix_phpcr_property

Fix bug preventing PHPCR property names being used from mapping