Add option to not use native file dialogs

Thanks to Patrick Chevalley for updated french tranlation

settingsdialog.h

@@ -3,6 +3,7 @@
 
 #include <QDialog>
 #include <QSpinBox>
+#include <QCheckBox>
 
 class SettingsDialog : public QDialog
 {
@@ -15,6 +16,7 @@ private:
 
     QSpinBox *m_preloadImages;
     QSpinBox *m_thumSize;
+    QCheckBox *m_useNativeDialog;
 };
 
 #endif // SETTINGSDIALOG_H