Fix children translation based on the parent document.
(Before the children locale was the  request one)
Fix children translation based on the parent document.

Correction the way to retrieve locale : lukas review
Refactoring to use theUnitOfWork::getLocale() method
Add translation children tests
- add test on $doc->getChildren which already works before my modification
- add $dm->getChildren($doc) to test my modification of UnitOfWork
Merge pull request #226 from nicolas-bastien/fix_children_translation

Fix children translation based on the parent document.