The MaterialManager.materialsUpdated signal was only called once upon init and for the rest when a favourite was added or removed. So only the FavoriteMaterialsModel would need to listen to it.
Because the MaterialManager is being deprecated, the favourite materials model now just listens to the preferences changing instead, as it was supposed to be doing anyway.
Contributes to issue CURA-6600.
Did this so that models can be updated more often fixing bugs where when a material is set as "not favorite" in the favorites section, its updated accordingly in its "normal" section.
It's also the ground work for saving material section expansion to preferences.
Contributes to CURA-5378
I was hoping to completely nix the generic materials model (since it's basically just a brand "Generic", but then in the QML it has to be have the same in terms of sub-menus or fold-outs and that looked stupid (Generic -> ABS -> ABS)). So we keep that one for now. It is cleaner though.
Contributes to CURA-5162, CURA-5378
