kiwix-serve: title is not updated dynamically inside the viewer

[benoit74]

When document title is dynamically updated (e.g. by JS code, e.g. because ZIM is serving a Vue.JS SPA), the title of the viewer is not dynamically updated (e.g. in browser tab, but also in bookmarks, both annoying).

See for instance:

• https://library.kiwix.org/viewer#scalewaywebinars_fr_all/index.html => when you change video, the browser tab title is not updated
• https://library.kiwix.org/content/scalewaywebinars_fr_all/index.html => when you change video, the browser tab title is dynamically updated

Nota: this is somewhat related to #1120