Main window: Fix the option "Redo OCR on all documents"

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: Options "Redo OCR": update the index only at the very end

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Frontend: confirmation dialog: Fix warning regarding use of obsolete attribute type=

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