Improve favicon

[kelson42]

We have only a minimal support of favicon. Different devices need different favicons, check with https://realfavicongenerator.net/favicon_checker?protocol=https&site=library.kiwix.org%2Fcontent%2Fwikihow_fr_maxi%2FAccueil

[rgaudin]

This probably deserves a Wiki page on overview with the decisions to make and implementation. I believe that most websites we scrape (as does wikiHow) don't respect those rules completely.

While all those options exists to provide flexibility to designers, to adapt icons to context, as we are just scraping, we won't do any creative work and are thus left with two options:

• copy when it exists
• resize/scale another one to the required size.

Now that's fairly easy (although arbitrary – using cubic downsizing) for generating icons that are smaller than the source we have but what about upscaling? Should we upscale icons so that all those checks are marked green or should we only provide the ones we can with same quality as what we got from upstream?

Beside this, it's important to note that choosing an icon is difficult. A lot of website have a favicon, maybe with various small sizes and a logo on their website that is different but available in a much higher resolution. As we don't have access to sources, we have to mangle with those both for the favicon(s) and the ZIM illustration(s)