Restore kiwix-tools 3.4.0 top bar (random button, search)

[holta]

@tim-moody I've changed /kiwix/ to /kiwix/viewer# in both places for now, as kiwix-tools 3.4.0 is now fully released, and as a result is now a part of fresh IIAB installs (as of a few hours ago).

(Is it possible you might prefer to move js-menu.yml to js-menu.yml.unused, e.g. if ./install-menu migrates away from using this file in future? Just a question; I don't know what's preferred.)

Context: kiwix-tools 3.4.0 requires a different URL to restore the top bar (for search, random button, etc) as summarized here:

• iiab/iiab#3412

[holta]

This PR was successfully tested on Ubuntu 23.04's latest daily:

• http://10.8.0.54
• http://sprunge.us/yZPusT?bash

[tim-moody]

breaks backwards compatibility, but not sure how to avoid it

[tim-moody]

how about a default vars variable kiwix_new_url: True

[holta]

Maybe just document that upgrading "pre-December" Kiwix and "pre-December" Admin Console should happen simultaneously?

(Each can be upgraded in a single line; certainly spelling that out for advanced operators is probably a good thing.)