Pickup an item in inventory

[fluffyloafie]

• [x] Implementation of the “Pickup item” packet
• [x] Send the packet to a player that is in the item's collection area, checking at each set_player_position
  • [x] Check if the item is within the player's pickup range at each set_player_position
  • [x] Send the packet
• [x] Destroy picked up entity
• [x] Add item to player/entity inventory