Purge container list

Add an item in the CL action menu "delete all containers"

A click on this item launch a confirmation window with the message "All containers of this list will be deleted. The never-published containers, will be deleted without any possibility of subsequent recovery" + two buttons "confirm" "cancel"

Click on confirm launch the delete process which is similar to the already "delete container" implemented, but iteratively until the list is empty.

Once the process is finished, a notification should be displayed to the user, with the same ajax "pop up" we use to notify the end of some processes
"process is finished"
"please reload the page"

There is no new engine to develop.