Changed the visualising of the ray-test a bit
Added sort-of-destructible walls. The walls don't obstruct shots or units, but can be hit by missed shots to test the removal. Walls have basically no health, as well.
When a wall is destroyed, it toggles its collision type to be an empty cell and prompts a rebuild of the entire contents grid, which is terrible.
This should call a rebuild of the wall mesh, which will hopefully be spatially divided such that I'm not rebuilding massive meshes with each change.