z-axis: support position delta and improve rod support

z-axis: support position delta and improve rod support

zaxis_delta_y and zaxis_delta_x shift the entire z-axis away from the
frame. The Wilson TS frame moves the z-axis 5mm in x and y, and this
allows generating compatible z-axis parts. The 2020 frame benefits from
shifting the z-axis outward -- if it is not, the motor won't clear the
side of the mounts for the Wilson TS rear frame braces.

An additional support for the smooth rod hole is generated if the delta
is set. The motor mount walls are also removed if needed.