Just like the QualityManagementModel, this class is intended to be used as proxy for the material management page in the preferences. I'm intending to move all relevant pyqtSlots from the material manager into this one. The advantage of this switch is that the material manager had no well-bounded scope and so tended to become a big mess of all sorts of functions. This one has a clear scope: serve as a proxy for the buttons you can press in the preferences screen for materials.
Contributes to issue CURA-6600.
Cast every sorting key to uppercase before doing this. Don't cast to lowercase or there will be problems with characters that don't have lowercase and with Turkish dotted i vs. undotted i.
Fixes#3460.
