Update labextension to JupyterLab 3

[jtpio]

Take two for #89

$ jupyter labextension list
JupyterLab v3.0.0rc10
/home/jtp/miniforge3/envs/gator/share/jupyter/labextensions
        @mamba-org/gator-lab v2.0.0-rc.0 enabled OK (python, mamba_gator)

The coveralls has been removed as it is broken.

TODO

• [x] Switch to jupyter-packaging
• [x] Add a new labextension3 folder for the lab3 federated extension
• [x] Update the navigator (also update the server app part)
• [x] Remove resolutions
• [x] Decide whether to keep the tgz, or only the lab3 federated bundle and only one labextension dir, see: https://github.com/jupyterlab/jupyterlab/issues/9277#issuecomment-725585673
• [x] Standalone navigator in Binder is broken

[github-actions[bot]]

:point_left: Launch a binder notebook on the branch jtpio/gator/lab3

[jtpio]

We might want to have this PR in first: https://github.com/fcollonval/jupyterlab_toastify/pull/13

To help align the versions of React.

[jtpio]

Decide whether to keep the tgz, or only the lab3 federated bundle and only one labextension dir,

It might not make sense to keep the tgz as part of the data files, if we end up updating all compatibility ranges to 3.0.0 for the lab packages. 3.0 users will use the federated bundle directly.

The tgz is only useful to lab 1 and 2 users.

For lab 2 users, the readme can mention the extra command to install the extension:

jupyter labextension install @mamba-org/gator-lab

[fcollonval]

We might want to have this PR in first: fcollonval/jupyterlab_toastify#13

To help align the versions of React.

Done 😉

[fcollonval]

* Remove `resolutions`

This seems to be done.