</br> instead of <br/> renders fine in the browser but not in an epub

1. Renaming episode_title to episode_navbar since it now has dual use.
2. Removing hr elements that look odd with footer nav arrows.
3. Conditionalizing display of episode title.
4. Modifying layouts for breaks and episodes to include the footer nav arrows.

1.  Fixing image link in `setup.md`.
2.  Regenerating all-figures.

Closes #42.

Using `site.github.url` to refer to the repository fails to load resources when the GitHub Pages site is accessed via HTTPS, because `site.github.url` is `http` protocol.  This modifies loads of CSS and Javascript files to always use `https`.

1.  Use site.root for root path if set, otherwise use site.github.url.
2.  Display extra files for workshop-template repo as well as for lessons.