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.
Actually, what is going on here? You should just need to template the tag in, and nothing else. What is the purpose of the `<div>` with the plot id as a CSS element id? I don't think that is needed (or advised).