Add possibility to move nodes

[daniel-wer]

Add the possibility to move nodes by adding an action/reducer and by making the WebGL buffer updater (skeleton.js) update node and edge positions.
The active node can be moved using "Ctrl + Arrow Keys" or by using "Ctrl + LeftMouseDrag".

URL of deployed dev instance (used for testing):

• https://movenodes.webknossos.xyz

Steps to test:

• Open a tracing and move nodes using the mentioned keyboard and mouse controls.

  • Does it work in each viewport?
  • Is the node position persisted after a reload?
  • Does it work for branchpoints?

• Testing the merger mode:

  • open a skeleton tracing with a segmentation layer
  • enable the merger mode and create two nodes that merge to segments
  • Now move one of the nodes around. The mapping should update as expected.

Issues:

• This will allow users to easily correct ground truth skeleton data. Previously one needed to remove a node, add a new node and reconnect the split trees.

---

• Updated (unreleased) changelog
• [ ] Updated (unreleased) migration guide if applicable
• [ ] Updated documentation if applicable
• [ ] Adapted wk-connect if datastore API changes
• [ ] Needs datastore update after deployment
• Ready for review

[daniel-wer]

• Use Ctrl + MouseDrag instead of Shift + MouseDrag, because Shift + Click selects a node and the potential to mistakenly move nodes feels rather high
• Undo buffer should not be completely filled with updateNode actions, take latest instead

[daniel-wer]

@MichaelBuessemeyer Just a small note regarding your last two commits. Also, please add the new shortcuts to the shortcut overview page :)

[philippotto]

Awesome stuff!! Works very well 👍

Moving a node can be a tad laggy, but I think this is alright for this feature. However, I noticed two things which should probably be improved before merging:

• moving does not work in a hybrid tracing (have a look at getPlaneMouseControls in plane_controller.js)
• the move-shortcuts don't repeat when being pressed down. If I want to move a node by 20 pixels, I have to hit the shortcut 20 times?

[MichaelBuessemeyer]

Also, please add the new shortcuts to the shortcut overview page :)

good catch 👍

[MichaelBuessemeyer]

@philippotto I applied all of your feedback except one thing (see my comment). Could you please have a look at this PR again?

[normanrz]

• Btw moving nodes does not seem to work with merger mode yet.

[MichaelBuessemeyer]

@philippotto I just adapted the merger mode to work correctly when nodes are moved. Could you please check this PR again? I added a section on how to test the merger mode to the description. The description is rather easy 😄

[philippotto]

Awesome! Works very well. I left some smaller changes, but apart from these, the PR should be good to merge :)