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 in this case it does. If this was a real app with 200 plots to contend with I'd reach for something like this but I think here it's better to make the individual cases as clear as possible and "grouped together" for users.