Updated snow plow

- Tabs are taller and thicker
- Add a base to the tabs to help with stability during printing
- Make base of plow flat (comment out tilt) so this can print.
- Use flat/truncated teardrop shape for holes, for better printing
- Include a cutout section to insert a magnet (if the user wants to
  use a magnet to hold the plow in place).
- Slight tweak to plow shape to accommodate magnet cavity.
- Slight tweaks to radius values to account for shrinkage and
  slightly larger magnets (based on test print and real train sizing)
- Documentation