Layout 2D along X,Z

This lib is genius. A gem on GitHub.
Quick question on the physics settings:
```
this.physicsSettings = {
dimensions: 2,
timeStep: 0.5,
gravity: -12,
theta: 0.8,
springLength: 20,
springCoefficient: 0.8,
dragCoefficient: 0.9,
};
```
I noticed that starting nodes in a flat plane, initial positions scattered on X and Z plane, everything lays out flat as expected. ( like on a table top ). But adding nodes at run-time everything goes 3D.

Is there a way to set dimensions:2 and have the constraint be the X and Z axis instead of the X and Y axis?
It appears they capability is already in the lib. Just not sure how to access it.
Setting dimensions to 2 seems to constrain it along X and Y. Would love to constrain it to X and Z.

Cheers and Thanks You!

Start by tracing the physicsSettings dimensions option and the path used when nodes are added at runtime. Verify whether the existing two-dimensional constraint can be configured for X and Z instead of X and Y; done means newly added nodes remain on the X,Z plane with dimensions set to 2.

Written by the indexing model from the issue text.