At the moment, only the mouse can be used to focus and answer a chat
notification.
This adds a new keybinding (defaults to <Super>+n) to focus and expand
the active notification.
https://bugzilla.gnome.org/show_bug.cgi?id=652082
This is a workaround for power users for the "Show Apps" button
placement being too inconvenient to press at the bottom of the
dash favorites list.
Unity also uses Super+A to show the Apps lens.
https://bugzilla.gnome.org/show_bug.cgi?id=685738