VoxelSet voxel IDs shift whenever removing a voxel

[ClarkThyLord]

Currently, a VoxelSet shifts all of its voxel IDs each time a voxel is removed. This is due to an oversight when designing the way in which voxels are stored and managed. A fundamental reworking of how voxels are stored and managed within VoxelSets is needed to avoid this and achieve the desired functionality.