List all available icons in Makefile.am
List all available icons in Makefile.am

This mismatch was causing e.g. gtk-caps-lock-warning.png to show
up as missing image in entries.

At the same time, sort the icon list alphabetically.

johne53/MB3Gtk-2,johne53/MB3Gtk-2,Unity-Technologies/gtk,Distrotech/gtk,johne53/MB3Gtk-2,johne53/MB3Gtk-2,Distrotech/gtk,Distrotech/gtk,johne53/MB3Gtk-2,Distrotech/gtk,Distrotech/gtk,Unity-Technologies/gtk,Unity-Technologies/gtk,Unity-Technologies/gtk,Unity-Technologies/gtk