Update KLettres French documentation screenshots.

In a default KDE installation, use KSnapshot to do all the 9 screenshots to match the English ones from https://projects.kde.org/projects/kde/kdeedu/klettres/repository/revisions/master/show/doc (all .png files). Instructions about screenshots: http://l10n.kde.org/docs/screenshots.php.

Expected results: The 9 screenshots in French interface are up-to-date with current KLettres interface and current KDE default style and default window decoration.

Prerequisites: KLettres installed with French interface, KSnapshot."