Added "overlay" functionality for player/NPCs.

New tileset IDs:
- overlay_worn_{ITEM ID}, overlay drawn over the character when the item is worn
- overlay_wielded_{ITEM ID}, overlay drawn over the character when the item is wielded
Removed superfluous null-check for worn items.
Fix draw_entity_with_overlays return type.

Function doesn't return anything.
Replaced item.type->id with item.typeId() in player::get_overlay_ids()
fixed scrolling in keybinding window
When loading active items, increment the active_item_count.
Remove outdated comment.
blockhead tileset: add missing entry for 't_concrete'
Blockhead tileset: add missing 'bg' to 't_concrete' and fix whitespace
Canvas bags and sacks, and crafting them.
Commercial fertilizer (solid) coming in canvas sacks as opposed to plastic bags.
Italian seasoning, black pepper, and seasoned salt coming in canvas bags.
SAI posts and fungicide in plastic bags
Guard rearmed

I am surprised no one tried putting rifle in the holster.
Merge remote-tracking branches 'dda/pr/8993', 'dda/pr/9031', 'dda/pr/9046', 'dda/pr/9050', 'dda/pr/9053' and 'dda/pr/9054' into dda-master

* dda/pr/8993:
  Replaced item.type->id with item.typeId() in player::get_overlay_ids()
  Fix draw_entity_with_overlays return type.
  Removed superfluous null-check for worn items.
  Added "overlay" functionality for player/NPCs.

* dda/pr/9031:
  fixed scrolling in keybinding window

* dda/pr/9046:
  Remove outdated comment.
  When loading active items, increment the active_item_count.

* dda/pr/9050:
  Blockhead tileset: add missing 'bg' to 't_concrete' and fix whitespace
  blockhead tileset: add missing entry for 't_concrete'

* dda/pr/9053:
  Italian seasoning, black pepper, and seasoned salt coming in canvas bags.
  Commercial fertilizer (solid) coming in canvas sacks as opposed to plastic bags.
  Canvas bags and sacks, and crafting them.

* dda/pr/9054:
  Guard rearmed
  SAI posts and fungicide in plastic bags