New pattern: pat-cookietrigger

See https://github.com/plone/Products.CMFPlone/issues/282

This pattern now contains the legacy JS from [plone_ecmascript/login.js](https://github.com/plone/Products.CMFPlone/blob/master/Products/CMFPlone/skins/plone_ecmascript/login.js)

Basically you put a class **pat-cookietrigger** on any DOM element and if cookies are enabled, the element will be hidden and if cookies are disabled the element will show.

ping @vangheem or @thet