No Support Rack-Mount Frame

Downloaded the 1U rack-mount Raspberry Pi holder by russross (https://www.thingiverse.com/thing:4125055). However my printer isn't great at printing supports, so this is a modified version of the the frame which should be possible to print without any support structures.

Changes include:
- Smaller bridging area
- Fewer 90 degree angles, including the areas surrounding the threaded bar.

The frame should print best on its back end.