Main window: forgot to define the priority of some jobs

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: label creation: display a progress bar while fiting the estimator of the label with all the documents

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: cosmetic: 2x info() --> debug()

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