Fix site for new Apache CSP

Some parts of https://flagon.apache.org/ are broken since the new apache content security policy (https://infra.apache.org/csp.html). The new CSP blocks all third party content, so the jQuery, D3, fonts etc. references in the site code fail. One solution would be to download needed packages and host them in our source, but it would also be worthwhile to prune the site's third party dependencies.

Inspect the site code for references to jQuery, D3, fonts, and other third-party content, then compare them with the Apache CSP requirements. Done means the affected site parts work under the new policy, with needed packages hosted in the source and unnecessary third-party dependencies removed where appropriate.

Written by the indexing model from the issue text.