Customiser: Justblair's Parametric Cylindrical Battery Dispenser

While eminently useful, I felt that this item needed slight improvements. The original version suffers from not entirely satisfactory battery retainment when loaded: bottom battery can be pushed out by the weight of the batteries above. This was solved with a change to the shape of the dispenser snout.
For adjusting holder position after mounting, to allow compensation for battery length tolerances, slotted mount holes have been added. Their length or presence is configurable, and allows oversi