add z axis with stepper support

[i-make-robots]

Is your feature request related to a problem? Please describe.
Some pen holders use a stepper motor for lifting the pen off the paper.
Instead of generating M280 P0 S[angle] for this type the gcode should say G0 Z[angle]

Describe the solution you'd like
add a parameter to plotter settings and plotter settings panel. test it saves correctly. test it generates different gcode depending on the setting. check the new code generated is the correct code.