Fix mapping activation confirmation

[daniel-wer]

A breaking change in an antd minor version update led to the Popconfirm no longer appearing before/after the context menu was hidden. I did not succeed trying to stop the propagation of the event that hides the context menu and even if that would've worked, the context menu would've had to be closed manually after the Popconfirm was canceled/confirmed.

Instead, I switched to a Modal.confirm which appears even after the context menu is hidden, shows a spinner while the async action in onConfirm is performed and arguably looks better :)

URL of deployed dev instance (used for testing):

• https://fixmappingconfirm.webknossos.xyz

Steps to test:

• Open a dataset with a meshfile that was computed for a specific agglomerate file (test-agglomerate-file dataset)
• Rightclick on a segment - Load Mesh (precomputed)
  • There should be a confirmation modal which activates the respective mapping before loading the mesh iff it is confirmed
  • If the correct mapping is activated already, no confirmation modal should be shown
• Do the same from the segments list

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

• Updated (unreleased) changelog
• Ready for review

[philippotto]

Awesome :) This is probably the cleanest fix 👍