[table view] allow to set None in 'headers', meaning the label should be fetched from the result set as done by default (closes #1931533) the point of this is to avoid having to define the whole headers list when only some of them have to be defined.

#! /bin/sh -e
 
case "$1" in
    purge)
	rm -rf /etc/cubicweb.d/
	rm -rf /var/log/cubicweb/
	rm -rf /var/lib/cubicweb/
    ;;
esac
 
#DEBHELPER#
 
exit 0