cubicweb #2718217 [uicfg] reload bug: on reload, customized uicfgs just vanish [done]

and we fallback on the default values

this is likely because the modules get wiped at reload and the singleton uicfg are recreated, but those cubes (all of them) that do::

pvs = cubicweb.web.views.uicfg.primaryview_section

now have a reference to the old object

done in3.16.1
load left0.000
closed by#d94d3a3ba586 [cwvreg] complete cw.web.uicfg cleanup callback (closes #2718217)