SphereBot redrawn

I wanted to make a few modifications to nglasson's eggbot for my own build. As a first step, I've redrawn it in Fusion 360 because I don't like working in Sketchup (sorry Sketchup fans), and Fusion's STL output is of higher fidelity. This model is mostly faithful to the original, except I've modified a few screw sizes to fix interference. I've also added the steppers, servo, and all hardware to the model assembly to help in ordering parts.

**Update**: v2 has a few updates and fixes:

* The pen arm shaft coupler axle hole has been resized to fit the axle on my stepper motor (5mm around, flat face inset .5mm, .1mm outside clearance).
* The outer bearing holder has been integrated into the right end plate. The idler must now be on the right, unless you mirror this, but now you can replace four long screws with one medium one. This should be printed flat side down with support for the bearing hole.
* The inner bearing hole in the end plate has been shrunk from 24mm to 22mm t