Improve warning-toasts regarding segmentation

[philippotto]

Mailable description of changes:

• Segmentation-related warnings will be shown less frequent (e.g, not for skeleton tracings when there are multiple resolutions for segmentations anyway).

URL of deployed dev instance (used for testing):

• http://improvesegtoasts.webknossos.xyz

Steps to test:

• ensure no warnings are shown for datasets without segmentation
• for a dataset with only one segmentation-resolution:
  • no warning should be shown for resolution 0
  • ensure that a warning is shown regarding downsampled buckets, when being zoomed out a bit
  • ensure that a warning about unsupported volume is shown as soon as no segmentation is displayed anymore (zoom out further for that)
• for a dataset with multiple segmentation-resolutions:
  • no warning should be shown for resolution 0
  • ensure that a warning about unsupported volume data when being zoomed out a bit in volume mode (for view + skeleton, there shouldn't be a warning)

Issues:

• fixes Improve toast warnings regarding segmentation + zoomlevel #2699

---

• Ready for review

[daniel-wer]

Works like a charm! 🎉