Use l10n/i18n latest standard

Created by: samuelsov

Fixing https://github.com/CiviCooP/org.civicoop.documents/issues/12

To test :

• download .po file from transifex
• compile .mo
• put the file in /l10n/fr_CA/LC_MESSAGES/documents.mo

Before : translation is not working (only existing translation in Core might works)

After : all the translation in the mo file are used

Note : There is no new feature, only translation normalization.