Disable people

Following a feature request (Bug 459499), this merge request implements the possibility to deactivate certain people for face recognition. This can be done in the settings where a new "Face recognition" tab is added (more options can be placed there in the future). Faces of deactivated people will not be recommended when starting a "Recognize faces" process. Moreover, faces of deactivated people are not used for training the recognition model.

I would like to add more options and parameters in the new "Face recognition" tab to improve face recognition in the future.

As usual: Thanks for considering and your help!