Needs: added sensor for detecthing if we reached the notch

[hzeller]

If the current on the stepper is too low, it might be that there are lost steps when it needs to pull hard on incoming bands. There should be a secondary test to make sure that is the case, e.g. a fork light barrier. When at the end of a cycle, we have not reached the notch yet, it keeps turning until it is; possibly recording how often this happens and store in firmware for later adjustment of current.

Also: this can be used to auto-align the wheel when the motor is switched on.