Moveoff demo -- fixed retract on single axis (Z)

Demo:
  1) Start linuxcnc using the 6_zretract config
  2) A pyvpcp panel includes a checkbutton
     to enable fixed offsets on program
     pause.
  3) Start program
  4) Pause program
  5) A moveoff_gui display (with no controls) will
     appear showing the current Z offset.  If the
     checkbtton was set to enable offsets, the
     offset will be applied immediately.  If the
     checkbutton was not set, enable the checkbutton
     to apply the offset.
  6) Toggle the checkbutton to OFF to
     remove the fixed offset and resume the program.
  7) The fixed offset will be removed after
     a delay to allow for spindle reactivation.
     Typically, the spindle would be gated
     off for the duration the mv.offset-applied pin.
     The delay allows time for the spindle to resume
     speed.
  8) Toggle the sim_pin external_enable switch to
     1 (ON) to allow offsetting at the next program
     pause -- or leave it OFF to require its
     activation on the next program pause.

The ini file sets:
  1) offset amount and its velocity and acceleration
  2) state of the external-enable signal at startup
  3) autoresume delay interval
  4) location and size of the moveoff_gui display

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Moveoff_gui options:

  onpause  -- offsets when program paused
  local    -- local controls

Moveoff component installed and connected using:

  [HAL]HALFILE = LIB:hookup_moveoff.tcl

For additional info:

   man moveoff  ------ moveoff component
   man moveoff_gui --- moveoff sample gui