cubicweb #3274672 provide a "modal" main template [validation pending]

IOW a main template that just renders the view.

For the record, the relationwidget and resourcepicker cubes need it (they will of course provide their own thing till this exists in core).

prioritynormal
typeenhancement
done in3.18.0
load0.100
load left0.000
closed by#4a668dcfa0a0 [views/templates] provide a modal main template (closes #3274672)
patch[views/templates] provide a modal main template (closes #3274672) [applied]