Two issues: `center-of-mass` returns `y` as up, and calculates flipped `z` value

[jgomez720]

Description

Two issues:

• The y value is returned as up, when it should be z
• The current z value (which is forward), is being returned as its opposite. (flipped axis)

Version

0.2.108

Example

This model should return x=10, y=9, z=2.5

actual response:

{
  "center_of_mass": {
    "x": 10.0,
    "y": 2.5,
    "z": -9.0
  },
  "output_unit": "in"
}

y is currently up, and the z is flipped. Everything should be positive in this example.