Prusa Mini Z Axis Bottom redesign

A redesign of the Prusa Mini Z Axis:

• Remove the integrated electronics box; want to print it separately so can more easily adapt to new electronics
• Remove the need for the metal plate at the base of the Z axis, replacing it with a single piece of plastic. I've found it to be strong enough so far.
• Use a 3D printed T Nut for the 3030 extrusion - I couldn't get metal ones quickly.
• Two machine screws on the top of the extrusion instead of one.