Isolate meshes by layer and remove old mesh-storage code

[philippotto]

URL of deployed dev instance (used for testing):

• https://___.webknossos.xyz

Steps to test:

• create an an annotation with two volume layers (without fallback is the easiest for testing)
• create a segment 1 in both layers (should be at different positions ideally)
• name these segments differently
• save
• load isosurfaces for both
• both segments should appear in the 3D viewport (regardless of layer visibility) <-- maybe we should change that in the future, but I think it's independent of this PR

Issues:

• fixes Meshes of separate volume layers are not isolated properly #6952
• contributes to Remove or fix persistent mesh import of "ordinary" STL files #5633

---

(Please delete unneeded items, merge only when none are left open)

• Updated changelog
• Adapted wk-libs python client if relevant API parts change
• Removed dev-only changes like prints and application.conf edits

[philippotto]

@fm3 What do you think about removing the mesh-storage related code in the back-end in this PR (see ##5633)? When I started rebuilding the code for proper isolation, I ran into the old, (mostly) dead code and removed it. Do you have capacities for this? Or would you like to postpone it?

[fm3]

The last post in the issue stated that we might want to reconsider if we really want to remove that feature (?)

Either way, I’d defer removing the backend code in order not to block this PR until I have time. But I will gladly do so in a follow-up PR

[philippotto]

The last post in the issue stated that we might want to reconsider if we really want to remove that feature (?)

Yes, but I'd put the emphasis on "might" 🙈 The last feedback we got on that topic was over a year ago (and in total it was by one user). The feature was already effectively removed, anyway, and I don't really see big reasons to reintroduce it. For the mentioned use case, one could also find other ways (e.g., create a volume annotation to get the desired shape as an isosurface or allow to create a plane with a skeleton).

Either way, I’d defer removing the backend code in order not to block this PR until I have time. But I will gladly do so in a follow-up PR

Ok, cool 👍

[MichaelBuessemeyer]

Thanks for this bug fixing & refactoring 🥇 🦖 .

I only left some small suggestions (renaming & moving a method into another class). As they are not much work / shouldn't be risky changes I already gave you an approve :) I hope that's alrighty.

I did not check, whether you removed every single method that is not needed anymore is removed. I hope that's ok. If you want me to also check this, just ping me :).