Translation does not propose all data-languages due to typo

[twistoliver]

The "translate" feature in UI does not propose all data-languages proposed in user-settings data-languages.
The displayed lists differ due to the use of 2 different functions:

• tao_helpers_I18n::getAvailableLangsByUsage for translation
• tao_models_classes_LanguageService::singleton()->getAvailableLanguagesByUsage for user settings

The first function returns bad values due to the presence in database of two different properties:

• tao.rdf#LanguageUsages (defined in tao.rdf)
• tao.rdf#languageUsages (used in helpers\translation\class.RDFUtils.php: $doc->createElementNS($base, 'tao:languageUsages'); and in XML tag used in lang.rdf files)