Auto Level Mount Holder Acrylic Geeetech Prusa I3 pro B

Another Auto Level Holder, very simple but solid design.
Fitting exactly the Acrylic Geeetech Prusa I3 standard extruder mount and no need for a metal bed if using a 8 mm inductive sensor.

```
#define X_PROBE_OFFSET_FROM_EXTRUDER -18
#define Y_PROBE_OFFSET_FROM_EXTRUDER -44
#define Z_PROBE_OFFSET_FROM_EXTRUDER 0
```
To get zero z-offset my inductive sensor has about 5.20 mm distance to the glass surface. Distance and offsets are not by design but measured so may differ a little.

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