This change will make the "PROBE" command actually reply with the
z-position where the probe triggers. As this command is called
internally for the BED_TILT_CALIBRATE and Z_TILT_ADJUST those commands
will also give a response while probing, which I see as advantage over
the silent operation.
This change also lets one define some gcode for a repeatable probing
test to meassure the quality of the sensor and overall probing accuracy.
Signed-off-by: Hans Raaf <hr-klipper@oderwat.de>