High Stability Parametric Z-Probe Holder

I found it critically important to have a sturdy and balanced design for a z probe holder, the original was quite flexible. This design aligns the microswitch contact point exactly below the servo rotation pivot for max stability. The design is parametric so you can modify the length of the probe from servo to microswitch. Make it as short as possible. I do use it on makerfarm, but I printed new x carriage assy so stock will probably need to be longer.

I haven't found much use for auto-bed levelling as I prefer a level build platform, but I did find it useful for scanning the surface of the bed (which revealed that my X rods were bent) and its great help for measuring and manually levelling each corner.

I did have to make changes to the marlin V1 firmware branch to support this fully. If someone needs it I can post a fork.