Add pyodide version of calculator

[bmaranville]

This PR:

• modifies nact.py so that the cgi import is lazy (not compatible with pyodide, can't be imported)
• adds a new single-page app index_pyodide_optimized.html that shows the interface immediately, but loads pyodide and dependencies in the background in a webworker
  • if a user clicks calculate buttons before the worker is ready, a spinner appears until the calculator is loaded, then it shows the result
• adds some deploy scripts for adding this as a static resource on a traditional webserver
  • vendors pyodide, jquery, and wheels.

[pkienzle]

We don't want to maintain four different versions of index.html. Any way to consolidate them, or to move common components into other files? Moving the javascript and css to separate files is an obvious step. Can the html be set up as an include as well?

[bmaranville]

Sorry, two of those are not really needed and can be dropped... html includes aren't really a thing anymore, but yes the CSS can be shared, as can most of the JS.

[bmaranville]

superseded by #24