Fix duplicate entries in nav.html and default.html

Changed `site.html_pages` to `pages_list`, to repeat the nav order of the grandchildren in the nav panel.

Deleted a spurious line from a previous version.

Co-Authored-By: Patrick Marsceill <pmarsceill@users.noreply.github.com>

Co-Authored-By: Peter Mosses <18308236+pdmosses@users.noreply.github.com>

feat: adds option to open aux links in new tab

Create ci-master.yml

Default nav order

Added a configuration option to determine whether the sort order is case-sensitive.
The default is case-insensitive.

To test:
- open `/just-the-docs/docs/utilities/` in the browser,
  and check that the navigation links in `Utilities` are sorted alphabetically;
- in `docs/utilities/layout.md', change the preamble to `title: layout`,
  and check that the  links in `Utilities` are still sorted alphabetically;
- add `nav_sort: case_sensitive` in the configuration file,
  and check that the link to `layout` is now listed last under `Utilities`.

Added `.jekyll-cache`

Merge branch 'improvement/custom-themes' of git://github.com/SgtSilvio/just-the-docs into SgtSilvio-improvement/custom-themes

Fix Stylelint workflow and add prettier