Add woollen/patchwork staircase assets

[LauraFoglia]

The last row of this spritesheet is from this asset pack: https://pixelfrog-assets.itch.io/tiny-swords

The rest of the rows were modified to match the wooly/patchwork style of the game.

We need new tiles to replace the staircase ones.

XP Summary (total 200)

Subdomain	Skill	XP
Art: Aesthetics & Visual Design	Problem Solving	50
Art: Aesthetics & Visual Design	Creativity & Design Thinking	75
Art: Aesthetics & Visual Design	Technical Literacy	75

[wjt]

We no longer have a staircase in the world map. (Stephen is adding one to some other level, but it's a staircase to nowhere at the edge of the scene: just a prop.)

So I think this is less important now. Retitling.

[wjt]

The team who created “El Juguete Perdido” used stairs, as does “Stella and the Missing Star”.

The height transition is a bit hard to see but that's probably an inevitable consequence of trying to fake depth with flat tiles. Still it would be nice if we could make them match better.