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.
Maybe call `.render` in the `Population` initializer (and call it `._render`)? Or just put the code in the initializer? What is the purpose of separating the steps like this?