Enhancement - Allow setting of retract height after probing surface.

[J-eremy]

Allowing the z height location to be modified after using the probing widget would greatly improve workflow.

After probing for the Z-height, Generally the next step while working with wood is to put the dust boot back on.

With the current configuration, that requires manually raising the z up enough to fit the boot back on.

My recommendation would be to either allow a custom height to be set after probe, or just raise it back up near home after successful reading.