https://bugzilla.gnome.org/show_bug.cgi?id=672909
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
As some keybindings are now provided by gnome-shell rather than mutter, it makes sense to expose those in System Settings. https://bugzilla.gnome.org/show_bug.cgi?id=671010