Sequential_Shifter

- based on http://www.thingiverse.com/thing:1513638

Changes from above are:
- Made the switch carriers correct width, they were original 32mm wide to fit in a 35mm slot.
- Altered the switch holders in order to accommodate a "guitar foot stomp switch" these are plentiful and cheap on ebay.

-added spacers to center the handle on the spindle, more elegant than using lots of washers.

https://youtu.be/A3stJl2Mb08