Make meshes better

[normanrz]

Epic for making meshes more usable in webKnossos

• [x] Meshfile v3 with draco support
• [x] Better lighting
• [ ] Precomputed meshes for annotations
• [ ] Visualize all meshes at once
• [ ] Download all meshes at once

[hotzenklotz]

• [ ] Isosurfaces: Ensure that isosurface is visible in 3D viewport #5100
• [ ] Show planes when 3D viewport is fullscreen #5226
• [x] Add Isosurface Support for Volume tracings with Fallback layer #4930
• [x] Persist seed position when downloading isosurface as STL #5103
• [x] Efficient mesh storage #4810
• [x] Tri-state data display in 3D viewport #5225
• [x] Screenshot for 3D view #5218
• [x] Mesh shading looks weird #5011
• [x] Jumping to isosurface position via shift+click in 3D viewport is broken #5220

(Converted from ZenHub)