Anet A8 SN04-N Auto Leveling Sensor Bracket w slidable cutout

This is a small rework of https://www.thingiverse.com/thing:2063521

Changes:
- changed through hole for the sensor cable to a side-slide for easier access (this way you don't have to remove all the wiring for the probe if you need to switch your bracket)
- mounting hole converted to slidable cutout (more range for the probe to be mounted on, mine was too close to the surface in the original design)

To connect the SN04-N probe I have decided to go for the optocoupler method to supply the