Main window: Fix all boxes visibility toggling

Signed-off-by: Jerome Flesch <jflesch@wyplay.com>
Main window: Change the text of the option "Show all boxes" depending whether the boxes are shown or not

Signed-off-by: Jerome Flesch <jflesch@wyplay.com>
Update english texts and french translations

Signed-off-by: Jerome Flesch <jflesch@wyplay.com>