Update proofreading docs to reflect current state

[daniel-wer]

Also, I enabled Shift + middle-click to load agglomerate skeletons in all tools, not just the skeleton tool as that is how it is documented and shown in the context menu.

URL of deployed dev instance (used for testing):

• https://___.webknossos.xyz

Steps to test:

• Follow the instructions in the docs to check that they reflect the current state of the proofreading tool
• Open an annotation on a dataset with an agglomerate mapping.
• Activate an agglomerate mapping.
• Use Shift + middle-click in any tool to load agglomerate skeletons

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

• Updated changelog
• Updated documentation if applicable
• Considered common edge cases

[hotzenklotz]

LGTM

[philippotto]

great 👍 the docs now don't mention that you can also do split/merge operations on the agglomerate skeleton. however, this might be fine, because we don't really want to encourage this in the long term? just wanted to note this..

[daniel-wer]

great 👍 the docs now don't mention that you can also do split/merge operations on the agglomerate skeleton. however, this might be fine, because we don't really want to encourage this in the long term? just wanted to note this..

There's this sentence just below the section that I changed:

In addition to the handy shortcuts available from the right-click context menu, users can also directly modify the super-voxel graph like any other skeleton to manually add/remove nodes and edges for fine-grained control.

I'd say that's fine :)