Keep viewer content usable while scenes are migrated (#469)

[Subomiadekunle]

Closes #469 (part of #463)

Keeps the old bone viewer content usable while content is moved into scenes.

What changed:

• The viewer shows a button to open any scene made from the bone you're looking at. In the Scene Editor, "Made from: ..." links back to those bones in the viewer.
• Bones that haven't been moved into a scene look the same as before.
• Items with no images (like the Skull views) now say there are no images yet, instead of "Please select a bone".
• Removed the leftover axis_body_(dens) item.
• Bone ids can have hyphens now, so 2nd-5th metatarsals finally opens. Ids with slashes or dots are still blocked.
• If you click between bones quickly, an old slow response can't replace the bone you're on.
• Gave the [Small Rock] Validate Migrated Scenes #468 validation tests a 30 second timeout, since they go through every item.

How to test:

• npm test (new tests: boneset-api/viewerTransition.test.js and templates/tests/viewerTransition.test.js)
• Open Ilium, import it into a scene, go back to Ilium in the viewer and click the scene button, then click "Ilium" under "Made from". Then open Ischium (not migrated) and the Skull boneset (no images).

The plan for retiring the old content will be a separate issue, like the notes on #469 say.

[mudabs]

Thank you. I will hold off on performing a code review. However, I would suggest performing a sync on the branch as I have merged newer changes and this might resolve the 4 conflicts.

[Subomiadekunle]

@mudabs I updated this branch with the latest main and fixed the merge conflicts by keeping both sets of changes.

I also updated one test helper. After #507, importing a bone no longer saves it to the scene right away; the scene only saves when you click Save. The old test assumed importing also saved, so I changed it to import first and then save. All tests pass now.