FW retraction is extended onto swap retraction invoked by 'G10 S1'.
Bookkeeping of the retract state of all extruders allows for having one
extruder fw standard retracted while another extruder is swap retracted.
An LCD menu item for the swap retract and recover length was added.
Having the non-active feeder motors powered on all the time is not
necessary. A feature to deactivate the unused feeder motors has been
implemented. The feature is enabled on default but can be switched off
in the configuration.
Dim3nsioneer