Anet A8 Servo Z-Endstop

The Z probe is mounted between the radiator and the extruder fan.
The microswitch, ground and + 5V supply are taken from the Z_MIN connector.
The control signal of the servo taken from SERVO0_PIN 27, it can be found on the LCD pin 3 connector.
My firmware settings (Marlin 1.1.x):
```
#define Z_MIN_ENDSTOP_INVERTING true

#define Z_ENDSTOP_SERVO_NR 0
#define Z_SERVO_ANGLES {127,5}

#define X_PROBE_OFFSET_FROM_EXTRUDER -30
#define Y_PROBE_OFFSET_FROM_EXTRUDER -27
#define Z_PROBE_OFFSE