DocSearch: Make sure the index schema is up-to-date, regenerate the index from scratch otherwise

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: Reduce box-related job priorities. They are not that important

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
DocSearch: Add the document date in the whoosh index (useful for searching)

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: Search field tooltip: Add infos on how to target specific dates

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

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

Conflicts:
	src/paperwork/backend/common/doc.py
	src/paperwork/backend/docsearch.py