[web/data] fix treeview regression (closes #3526466) Changeset 68cde7431c2c "[js] remove 3.9 bw compat (where apparently unused)" removed the use of form.callback from loadxhtml, which treeview relied on. Update to add a callback on the loadxhtml return value instead.

etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances