Update Field.py

Do not add a transaction_note to specify that a field instance was empty, just add an info message to the log
Update utils.py

Do not return the value that is () when empty, return an empty string managed by ', '.join(nvalues).  This way, we avoid that displayValue returns () when the selection is empty...
Update CHANGES.txt

Update change log regarding last changes...
Add tests for empty value in at_utils.translate.