Create a Box3d using left, top, front, width, height and depth

Property definitions

geometry $ Box3d :: ltfwhd
	# Create a `Box3d` using left, top, front, width, height and depth
	init ltfwhd(left, top, front, width, height, depth: N)
	do
		ltwh(left, top, width, height)

		self.front = front
		self.back = front - depth
	end
lib/geometry/boxes.nit:275,2--282,4