Implement file export as a gcode job upload method

Useful for saving to an usb-mounted smoothieboard or an sd card, instead
of manually saving to a fixed path each time.

Better error handling during serial connection errors

Add configurable option to blank laser during G0 rapid moves.

Add configurable option to blank laser during G0 rapid moves. Fixes issues in PR #38 for Smoothie boards

Turn laser off when doing G0 rapids

Fix power command missing on subsequent gcode exports after initial export

Fix Smoothieboard not responding when connected via serial

MakeBlock XYPlotter driver

Export gcode

Smoothieboard Support

Driver for a Goldcut cutting plotter 

It was written to support a Goldcut ABH 721 [Refine MH721, Jinka JK721]
Speed and pressure of the devices cannot be software-controlled. This is done on the device.

These devices are simple HPGL plotters, thus the driver should support many more devices.
Maybe helpful with t-oster/VisiCut#256

added travel feedrate setting

Marlin driver update