[WIP] Voxel saving

[ScottCSteinhauser]

Motivation and Context

It's important that voxel grid saving & loading is enabled in the habitat simulator in order to enable users to avoid recreating the same voxel grids multiple times.

As my internship comes to a close, I will not be able to complete this task, but wanted to share my code in case another developer would like to pick it up.

So far, this is just a set of some initial functions for the saving and loading - it is by no means complete, but offers a starting point for implementing this functionality once Magnum can save & load 3D EXR images.

The SVX file format will be used for saving the voxel grids: https://abfab3d.com/svx-format/#:~:text=The%20SVX%20format(Simple%20Voxels,ease%20of%20implementation%2C%20and%20extensibility.&text=The%20basic%20format%20is%20a%20Zip%20file%2C%20named%20with%20a%20.

However, our implementation will save to EXR files instead of png files, since png files cannot store float values (which is needed in order to store float & Magnum Vector3 grids).

Types of changes

• tinyxml2 is introduced here to write to and read from SVX files.
• Functions for loading and saving multiple voxel grids and their structure is provided. Much is still to needed to be done.
• A default constructor for creating a VoxelGrid from a filepath (i.e. a SVX file) is declared but not defined.

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