Allow recyclables to be stockpiled on the ground

This could be done via stackers exclusively (trucks driving on a pile of scrap metal is unrealistic), to allow us to stockpile recyclables prior to constructing the recycling center due to its "expensive" build requirements,

This will be complicated, because the content of the recyclables are determined at time they are created. Consequently, the game would have to retain this information even when the recyclables are stacked on the ground.