[migration] add_workflow now ensure the entity type is actually workflowable, and a new make_workflowable migration function is available to make an entity type workflowable (closes #1382720)

#!/bin/sh -e
if [ "$1" = "purge" ] ; then
        update-rc.d cubicweb remove >/dev/null
fi
 
#DEBHELPER#
 
exit 0