optimize page loading times

@mjpost mentioned SEO in #434. I had a look at the google search console done month ago and even though our sites are static, they are classified as moderately slow loading. I did some experiments and found out that it is due to our external dependencies -- it is fast once they are in the user's cache but takes some time on the first load.

I propose that we 1) host them ourselves to enable http/2 streaming it whatever and 2) minimize some of those, e.g. only package the part of the fonts we need.

Start by auditing the external dependencies used by the static sites and reviewing the Google Search Console findings and first-load behavior described in the issue. Identify which dependencies can be hosted locally or minimized, then recheck first-load performance; done means the selected changes are implemented and their loading impact is verified.

Rédigé par le modèle d'indexation à partir du texte de l'issue.