Multiple popups

The cookie popup is working fine at first glance, but every time you resize the window, then a new popup appears. The problem here is that there is no .once() which prevents behaviour.attach() from calling more than 1 time, so this issue could happen not just when we resize, but whenever another module call Drupal.attachbehaviours(). This is related to the issue reported, fixed and closed here https://www.drupal.org/project/eu_cookie_compliance/issues/2741837 but there is a fix just for 8.x, so I created this ticket to have a backport to 7.x-1.x.