Openturf throw fix & minor refactors (#2203)

changes:

Thrown objects will now fire Entered() on the turf they land on. As a result, they will now fall if they land on an openturf.
Openturfs now queue an icon update if something falls down.
/obj/item/weapon/ore_radar converted to use SSfast_process instead of a spawn loop.
Converted hand-held tanks' New() to Initialize().
Note: This PR allows grenades to be thrown down openturfs.

code/game/atoms_movable.dm

@@ -192,6 +192,10 @@
 	src.thrower = null
 	src.throw_source = null
 
+	if (isturf(loc))
+		var/turf/Tloc = loc
+		Tloc.Entered(src)
+
 
 //Overlays
 /atom/movable/overlay