I don't know what exactly caused this since it's impossible to trace. But the crash happened with a setting called 'dual_gcode' which currently doesn't exist in Cura. So I think it must be some plug-in that adds it. In any case, it's good to be defensive about this sort of thing. Good type checking would've caught this for us.
Fixes Sentry issue CURA-JB.
- Move machine related models to cura.Machines.Models
- Move printer device related models to cura.PrinterOutput.Models
- Other UI/GUI related modules in cura.UI