Modernize information about visualization and post-processing

[Gabriele Bozzola]

https://bitbucket.org/einsteintoolkit/www/pull-requests/10

https://github.com/nds-org/jupyter-et/pull/17

are two steps towards improving and updating the information about visualizing and post-processing simulations. The first is updates the website with a new visualization.html page that briefly describes kuibit and visit. The second adds kuibit to the ipynb tutorial for new users.

Comments are welcome.

[Roland Haas]

Website changes look mostly ok to me (one request to use “latest release” rather than “latest version” when referring to the ET).

Changes are requested for the notebook pull request.

[Roland Haas]

Applied as git hash 4155961 "index: latest version -> latest release" of www

[Roland Haas]

Applied as git hash d090d83 "Upgrade to 20.04 and use Kuibit." of jupyter-et