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.