Add get_wielded_itemstring, get_wielded_item, damage_wielded_item and make getacceleration visible in API

Create the necessary API for /giveme and /give and implement those commands; also sort out the scripts a bit

Fix active_object_count and active_object_count_wider not getting updated between ABM calls causing huge amounts of DMs and rats and stuff

Rename menu background to menubg.png, move unknown_block.png and unknown_object.png to client, make generating a placeholder image for the filename "" not cause an error