Add button to export SageNB notebooks to Jupyter

[iandrus]

Once #19877 is done, then we can add a button to help the user export them.

[slelievre]

ping

[jdemeyer]

What is this ticket about?

A button within SageNB to export the current worksheet as ipynb?

[kcrisman]

This is to put a button specifically in the Mac app which does this (perhaps for all worksheets, perhaps for one?).

[jdemeyer]

Why only the Mac app? Why not SageNB?

[kcrisman]

No reason, that would just be a different ticket, since the codebases for the two are quite separate.

[kcrisman]

So now that the sagenb export is available and #19881 is there, time to figure this out. I need to test #19881 functionality.

[kcrisman]

I think this is still necessary despite the opening message, because if you start the SageNB server from the menu item it doesn't automatically show you that initial exporting message again. So unless someone decided to do this the very first time, they might not see that message again.

[iandrus]

This is a duplicate of #22821.

[embray]

Closing tickets in the sage-duplicate/invalid/wontfix module with positive_review (i.e. someone has confirmed they should be closed).