Hygiene: Use Generic Overlay-footer template for links

* Used in Notifications and talk overlay for footer link

* Moved content to a new, generic template

* Moved less to Overlay.less (from Notifications)

Follow up: I21191a66968a3556601e6b7a3c193e3ff193b35d

Change-Id: I926d3d0c90bcf59c4fbe9e865355e16b60d061f8