Create the workdir when Paperwork starts / the config is changed, instead of when the first scan is done.

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: In case of scan error, fix the display of the error message

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Merge branch 'testing' into wip-progressive-doclist-display