Fixes multi-z stairs being invisible, shunts old stair sprites to the abyss in favor of the goon ones

[AMyriad]

Document the changes in your pull request

• Fixed icemeta stairs being invisible
• Killed our current structure/stairs sprites since they're old and nasty

Why is this good for the game?

Bug fix is good
current structure/stairs sprites are godawful and I don't want to see them mapped anywhere
also keeping them the same as turf stairs makes them more seamless, and helps height illusions

Testing

Yes

Spriting

Lots of these icons in the goon stairs file were inconsistent (like having differently set directions) so I changed it up a bit:

Old

New

Changelog

🆑
bugfix: Fixed multi-z stairs not rendering at all (see: icemeta)
imageadd: Multi-z stairs now look nice, like every other piece of stair in the game
imagedel: Tossed old multi-z stair sprites into the 9th circle of hell where they belong
experimental: Please report or @ me if you see any upside down stairs
/:cl:

[Moltijoe]

dark middle looks upside down to me

[Aquizit]

It's a "wall." I cannot move. The miner cannot go back up the stairs nor leave the ones they are on, and anyone outside cannot enter the stairs.

[AMyriad]

merging this with access overhaul to avoid conflicts