Simplify the extension

Two way forward to rely more on quarto and css functionnalities :

- Have a custom toc with quarto and css to replace lua filter and template partials :
- check unnumbered vs unlisted don't show up in toc
- update readme and template with unnumbered and unnumbered + unlisted level 1 heading

- Remove modules Compl :
- switch customMenu into extension_yml
- Footer : remove footer.html and replace with :
in _extension.yml : (check path to logos are ok)
```
footer: |

```
in insee-clair.css 👍
```
.reveal .footer .footer-logo {
height: 26px;
margin: 0 6px;
vertical-align: middle;
display: inline-block;
}
```