-tg- SpaceMove update

This commit updates the spacemove system to -tg-'s; All objects now drift
in space, not just mobs. A few hardcoded space checks have been replaced
with has_gravity(); So it applies to zero-G as well as space.

Spacepods no longer drift, because their snowflakey shitcode just doesn't
work. So they just move.

code/modules/shuttles/shuttle.dm

@@ -94,7 +94,7 @@
 	for(var/turf/T in dstturfs)
 		var/turf/D = locate(T.x, throwy - 1, 1)
 		for(var/atom/movable/AM as mob|obj in T)
-			AM.Move(D)
+			AM.Move(D, SOUTH)
 		if(istype(T, /turf/simulated))
 			qdel(T)