This PR brings the option to move the selector directly using
buttons of the MMU - obviously while the MMU is idle and no
filament is stuck in the selector.
Left/Right buttons move the selector Left/Right.
Middle button performs a LoadFilament (into the MMU) on the active slot.
With this PR a change of LoadFilament behavior is also introduced.
Now, LoadFilament spins the Pulley for infinite time while waiting
for either FINDA trigger and/or a button pressed.
D.R.racer