"aria-labelledby" for navigation panel entries and corresponding ids contain illegal whitespaces

Closed as a `Won't Fix`. Note that the initial issue with the `aria-labelledby` does not apply anymore because it got removed in an update to jstree.

For the incorrect HTML part, we discussed it at https://forum.xwiki.org/t/escaping-jstree-node-ids/18767 and came up to the conclusion that the cost (mostly in code complexity) would far outweight the benefits given that update to jstree.