Switch cell type from the cell menu

[jtpio]

Iteration towards https://github.com/jupyterlab/retrolab/issues/259

Update the menus to:

• Rename the top-level Run to Cell like in the current classic notebook v6
• Add submenu to change the cell type

RetroLab

Notebook v6

[github-actions]

👈 Launch a Binder on branch jtpio/retrolab/menus

[jtpio]

TODO: this should not affect the JupyterLab menus:

Reported upstream in jupyterlab/jupyterlab#11754

[jtpio]

A temporary workaround would be to add the menu items programmatically in the plugin instead of using the settings system.

[jtpio]

Let's merge, and we can investigate how to properly use the settings system as a follow-up (jupyterlab/jupyterlab#11754).

[jtpio]

@meeseeksdev please backport to 0.3.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 0.3.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -m1 04177343498723eec84e0547f28287262a3158fe

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR jupyter/retrolab#328: Switch cell type from the cell menu'

4. Push to a named branch:

git push YOURFORK 0.3.x:auto-backport-of-pr-328-on-0.3.x

5. Create a PR against branch 0.3.x, I would have named this PR:

"Backport PR #328 on branch 0.3.x (Switch cell type from the cell menu)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.