Added Editor folder to controls panel

[Yahiewi]

This PR adds the following features:
-New Editor folder in the controls panel allows users to add joints by either toggling on the "Editor Mode" (could use a better name perhaps) and clicking on the parent and child links, or selecting them from a drop-down menu. The user can then input the parameters for the joint and add it. The added joint (if applicable) will appear in the joints folder and users can use it to move the robot.
-Input validation is now enforced on everything but the color selectors.
-Removed the need to refresh after adding a joint, it's now added immediately to the joints folder.

[github-actions]

👈 Launch a Binder on branch Yahiewi/jupyterlab-urdf/joints

[IsabelParedes]

Thanks! Just a bit of refactoring needed.

[IsabelParedes]

Thanks for implementing all the changes!

I tested it with URDFs which include mesh files and the Link Selector with the cursor was not able to select the links. Could you double check? Thanks!

[Yahiewi]

That is weird.
I just double checked and the Link Selector worked fine for all the files I tested on except for Panda where it worked but was a bit finicky (I'm guessing it might be because of the dae files).
I also checked that the version I tested on is the same one here (Tried pushing but everything was up to date).
Perhaps you can ignore this PR for now since you finished reviewing it and test the other PR instead which has all the changes added in this PR.