Locally generated online docs do not match http://doc.qt.io

See patch set here for an attempt so sync things up:

https://codereview.qt-project.org/#/c/242008/

Noe that to successfully view the locally generated online docs, one still needs to:

• Update qt-module-defaults.qdocconf to include qt-module-defaults-online.qdocconf
• Run a local webserver on port 80, so that all the "//foo.com/" urls resolve to the http/https protocol, instead of file://
• Map that webserver to doc.qt.io in /etc/hosts, so that the fonts and other resources in the CDN are not blocked due to CORS. It would be nice if we could add localhost to the CORS list, or something like dev.docs.qt.io so that one can compare the local docs to the actual online docs