Move and extend axis_unhomed test to deploy/stow_z_probe().
Move and extend position store/restore to deploy/stow_z_probe().
Now all kinds of probes can use the 'E' parameter in G29/M48.
Allen key probes can be used now for grid and 3-point levelling.
Deploying the Allen Key probe uses big moves in z direction.
Too dangerous for an unhomed z-axis.
Throw a compile time error when we try to configure an
Allen Key probe homing to z-min and having no other z-min-endstop.
