Recover embed examples

fixes #1458 

This recover the embed examples: 2 scripts and the reveal-based flask-based embed-based application :wink:

I just opened this as an standalone PR because it is a group of related examples and I am reintroducing them as a whole, not just tiny fixes like we will push to the pre-release example PR.
I think `pop` may be misleading to users trying understand the example too. It's both used as local variable in `update_population` function and as global variable defined at the bottom of the file. Just as a suggestion, maybe setting a global ``pop = None`` with a comment that it'll be properly set later (or turning it a local variable) makes easier to understand?