Main window: Fix weird exception

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: When the thumbnails of a page has been generated, reselect it if necessary

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Settings window: Add widget to adjust the zoom level

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Settings window: Once the calibration scan is finished, re-display the previous calibration settings

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: Scan: Once labels have been predicted, refresh the label list to correctly display the new labels

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Merge branch 'testing' into unstable