Add challenge scenes

[wjt]

These are deliberately unfinished scenes to accompany some guides.

Place them alongside the NO_EDIT template since they are deliberately
minimally themed (and use the template player rather than StoryWeaver).

Resolves #2871

[manuq]

This is the first time in Dev Archipelago that players would see a template character instead of the StoryWeaver, and scenes that by themselves have no playability at all. I understand that they would depend on companion guides, as explained in the quest description.

In Dev Archipelago MVP we described:

The player has ultimate freedom to play and experiment with different testing levels, gyms, and simple ("toy") examples with the hopes of sparking inspiration for unique StoryQuests and other contributions to the Threadbare game.

So I wonder if the archipelago is suitable for this. Could these be templates instead? The first siblings of the NO_EDIT template? Maybe a brand new "Challenges" template?

Otherwise, what are ways to make these scenes playable before being edited, while still open-ended?

[wjt]

Putting them into dev archipelago was my idea. We could instead just put them into scenes/challenges and not have them reachable in-game, only in the editor. I'm fine either way!

Edit: I reread your comment. Interesting idea, they could be in scenes/quests/template_quests!

[github-actions]

Play this branch at https://play.threadbare.game/branches/endlessm/wjt/add-challenge-scenes/.

(This launches the game from the start, not directly at the change(s) in this pull request.)

[wjt]

I revised this to drop the playground elder, and put them alongside NO_EDiT.

@jgbourque wdyt?

[manuq]

Looks good to me! Waiting for @jgbourque to confirm.