Add changes to cnc and d2k.
Update engine fallback defaults.
Add half-step cell size to CellDebugOverlay.
Add dev command for `cells-hs` to toggle half-step.
This points out a possible flaw in our cell
	coordinates/offsets wrt TS.
Buildings and units are on different cell grids
	(mismatched by 0.5 cells).
Meaning units operate on a shifted grid (+/-)512
	on x and y.
This is fine for mods that use rectangle (square)
	cells but turns things ugly for
	diamond TileShapes.
Main visual case is TS subcells.