put filament lengths in preferences instead of ...

... extruded material lengths
removed virtual extruders for support and infill

one to go: Extruder1 is still an alias for Extruder0
removed last virtual extruder, now extruderNo == physNo
make the removal of the virtual extruders more robust

Keep the extruders that have ascending physical extruder numbers and
remove all others. (Instead of removing a fixed set determined by their
old number.)
moved DumpX/Y to PrintSettings
removed physical extruder number and ExtruderN_Address

also fixed usage of extruder.toString() in material comparison
created new class PrinterSettings for settings specific ...

... to a printer model and moved WorkingX/Y to it as bedSizeX/Y.