Feature: let Parsons problems include imports

[nmstoker]

I struggled to get Parsons problems that feature imports working but that feature might be useful, both for fairly simple Standard Library related examples (eg involving say import math) and for those involving other modules.

It should be feasible, so long as the modules to be imported to Pyodide are:

1. The Standard Library modules that Pyodide includes or...
2. Pyodide's additional built-in packages
3. Additional third party packages (so long as Pyodide can successfully load them as per here for PyPI or here for arbitrary URLs)

I've got a fairly basic solution that works for 1 (see below) and am having a look at 2 now. If 2 works then 3 shouldn't be that much harder but maybe 3 is adding too much complexity / risk of going wrong for a simple training tool?!

[pamelafox]

Did you have to make any changes for 1/2? For 3, we could add support for the most common ones, like numpy and pandas, if we agreed to only load them conditioned on the code needing them. It'd involve a hard-coded list of wheels I think.