Correcting a minor bug encountered by some users of the wikipedia API (api.php)

This version slightly improves the code speed.

This version is a bit more lightweight. Additionally, it improved the situation when you explicitly request to see the "mobile view" of a Wikipedia page on desktop (this is a very edge case, but I guess it might happen from time to time for some users). In this situation, the addon should no longer interfere with this specific kind of request, and should let you see the mobile view, without applying the "classic" layout to it.

This update brings several improvements:
**General improvements**
- In addition to Wikipedia websites, the add-on now applies automatically the classic layout to some other popular Wikimedia projects: Wikimedia Commons, Wiktionary, Wikisource, Wikidata, and MediaWiki. Other Wikimedia projects may be added in the future, depending on users' requests and the project size.
- The add-on no longer applies the "classic" layout to https://nostalgia.wikipedia.org, as it would defeat the purpose of this wiki, which is to offer an even older layout to readers (dating back to 2001).

**For more advanced users**
- The add-on now allows to manually override the "useskin=vector" parameter in the url if needed. For example, if you want to test what a specific page looks like with the 2023 layout, you can replace "useskin=vector" in the URL with "useskin=vector-2022", and reload the page. The add-on won't interfere in this case.
- For those who'd want to read the Wikipedia mobile version on desktop (even if this is probably an edge case), the add-on now partially takes that into account, even if not still perfectly.

This update fixes an issue that made it impossible to load the homepage https://www.wikipedia.org.

In short, this update fixes two issues:

- it reduces the load on wikipedia servers when visiting it with this add-on installed.
- it improves web navigation fluidity (e.g., using the "back" button in the browser while visiting wikipedia could create some issues, before this update).

A minor update relative to the license of the add-on icon. It does not affect any feature of the add-on.