Add/fixup html file for new prefab features

[mmore500]

• reorder javascript includes
• add new javascript includes
• update bootstrap version
• add our custom CSS file
• add a loading modal and prefab card into the starter code

[mmore500]

also <meta name="viewport" content="width=device-width, initial=scale=1.0"> into the head

[kayakingCellist]

I added theses changes in a new branch, prefab-links. When I was looking for the link to update Bootstrap CSS, I found links to updated Popper and Bootstrap js files. (https://getbootstrap.com/docs/4.5/getting-started/introduction/)

Should we add these too?

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/js/bootstrap.min.js" integrity="sha384-OgVRvuATP1z7JjHLkuOU7Xw704+h835Lr+6QL9UvYjZE3Ipu6Tp75j7Bh/kR0JKI" crossorigin="anonymous"></script>

[kayakingCellist]

The prefab-links branch will fail until Empirical's prefab branch is merged into master because using prefab tools requires the directory source/prefab/*.