Add non-Python interactive exercise examples

Hi Tom,

Let's add this to the book! It aligns well with what I will try to do in the coming couple days: add 'standard MUDE elements' as an example for all of us to build a consistent book (Issue #3). Definitely good to have Grasple and H5p included here. Can you add a page/chapter anywhere in the cookbook part? Would be great to have a sample exercise worked out in 4 different platforms: Grasple, H5p, JupyterQuiz, Admonition (my original book with answers in dropdown). What do you think?

Once we have the examples, we can all play around with them a bit, then by our two-week sprint in August reduce and implement just one or two of them.

Hopefully in the next week or two we will do a similar thing with Python-based exercises (this is going on in MR !7 (merged)).

You had these things listed in your prior commits: a. Requires installing https://github.com/dbalague/sphinx-grasple b. iframe doesn't load locally, only online

i think a is a build issue and can be solved by adding to the requirements file right? b can be solved by including the instructions from here