Pywwt version of wwt tour or sharing pywwt sessions

[philrosenfield]

I think we need a means to export a session that conserves interactivity (so beyond rendering an image).

In the wwt clients, this is a .wtt tour file. However, I think people who want to make tours should use the full web or Windows clients. (Tours render from scene to scene and in another issue, we can outline how to support going from a pywwt session to one of the clients for this purpose.)

For this, I think we should be aiming for something like sharing a qt script, or something inspired by what Altair or plotly do to embed interactive plots in websites.