Port 'Box' demo to Python

[rolandlo]

I followed the Javascript example closely. One difference lies in the append function, where the signal handler must take the button as a function parameter, but the call to append() at the end doesn't pass one. That's why I used default parameter None.
The code appears to work fine.

[theCapypara]

Thanks! There are a few things here I would like to be less verbose, but this would require restructuring some parts of the demo across all languages + a bit of verbosity isn't bad for demo code I guess.