Auto-clear even when no more jobs to print#220

Provide an option to auto-clear the printer even when there is not job left to print to that printer. This automatic clearing saves time when the operator picks up the prints from idle printers. Currently, the operator must manually clear those prints.

This would also be very helpful when using the printer’s fans to rapidly cool the bed. For example, the machine-end gcode can be set to turn the fans on high, and then the auto-clear gcode can turn the fans back off again. Currently, if there is not next job for this printer, the fans will stay on full blast, even after the bed is cooled, which isn’t ideal.