Raspberry Pi camera ball mount

This fits a ~14mm sphere like my [Prusa z-tower mount](https://www.thingiverse.com/thing:3103924) and [Monoprice Mini Delta mount](https://www.thingiverse.com/thing:3002701). I dislike Pi mounts that move with an axis so this places it right against the bed. It has room for a LED ring (available cheaply on ebay) for illumination to be mounted on front.