[Localization] Improve French localization (lang.fr.php)

[Dmitry Khomutov]

See lang.fr.php:

Not present strings: 'delete_old_builds', 'delete_all_builds', 'source_webhook_pull_request_updated', 'source_webhook_pull_request_approved', 'source_webhook_pull_request_merged', 'rebuild_now_debug', 'total_errors', 'php_tal_lint_warnings', 'php_tal_lint_errors', 'behat_warnings', 'sensiolabs_insight_warnings', 'technical_debt_warnings'.

Strings same than English: 'plugins', 'builds', 'date', 'commit', 'build_n', 'build', 'classes', 'coverage', 'codeception_feature', 'codeception_suite', 'codeception_time', 'suite', 'test', 'message', 'test_message', 'test_total', '5_mins', '15_mins', '30_mins', 'description', 'version', 'seconds', 'plugin', 'stage_test', 'committer', 'timing', 'normal'.

[Dmitry Khomutov]

Not relevant now.