removed BedTemperature, was unused
removed preference change listener and moved ...

... prologue/epilogue getters to printer settings
also removed copied preferences values in GCodePrinter.
reduced visibility of Preferences methods and ...

removed unused methods
switched on simulation plot when running on single file
removed unused constant values in GCodeExtruder

asLength, shortLength, minLiftedZ were just (switched off) constants.
reduced visibility of methods in GCodeExtruder and removed ...

... unused parameters and constants.
removed unused preference values
removed own implementation of Math.toRadians()
moved calculations of circle area into one place
moved ExtrusionSize to ExtruderSettings as nozzleDiameter
moved retraction distance to ExtruderSettings
moved extraExtrusion lengths to ExtruderSettings
moved extrude ratio and early retraction to ExtruderSettings
moved InsideOut and MiddleStart to PrintSettings
moved arcCompensation and arcShortSides to PrintSettings
moved FastEFeedrate and FastXYFeedrate to ExtruderSettings

as airExtrusionFeedRate and printExtrusionRate
moved Lift to ExtruderSettings
moved MaterialName to MaterialSettings
moved material diameter and color to MaterialSettings
moved InfillOverlap to PrintSettings