Large objects

So I just realized that LargeObjects and Fields are conceptually pretty much the same thing; they fill the same corner of the size-dynamics quadrant

	dynamic	static
small	Particle	?
large	Fields, LargeObjects	Obstacles

Theoretically, according to Jonas, who wrote the original code for both of them, LOs should have relevant boxes, but in practice they don't (although you can see in the code that at one point they should have had them; there is a disused field lo_boxes in the struct).

My suggestion is to deprecate LOs in favour of fields, because clearly no one has looked at the LO code in years until I did a couple minutes ago, while Ilias is taking good care of the fields & has even implemented 3D support