Ooze prevention:

- remove the infinite skirt
- added 'idle_temperature' in Filament Settings as an optional parameter
- the logic is changed: if idle_temp is present, it is used,
  otherwise it uses the old delta value from Print Settings
- TODO: the optional parameter is not well supported in UI

src/libslic3r/PrintConfig.hpp

@@ -769,6 +769,7 @@ PRINT_CONFIG_CLASS_DERIVED_DEFINE(
     ((ConfigOptionFloatOrPercent,     first_layer_height))
     ((ConfigOptionFloatOrPercent,     first_layer_speed))
     ((ConfigOptionInts,               first_layer_temperature))
+    ((ConfigOptionIntsNullable,       idle_temperature))
     ((ConfigOptionInts,               full_fan_speed_layer))
     ((ConfigOptionFloat,              infill_acceleration))
     ((ConfigOptionBool,               infill_first))