-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/reagents/reagent_containers/spray.dm

@@ -46,6 +46,7 @@
 
 	playsound(src.loc, 'sound/effects/spray2.ogg', 50, 1, -6)
 	user.changeNext_move(CLICK_CD_RANGE*2)
+	user.newtonian_move(get_dir(A, user))
 
 	if(reagents.has_reagent("sacid"))
 		msg_admin_attack("[key_name_admin(user)] fired sulphuric acid from \a [src].")