Allow Thunderbird to execute gio-launch-desktop helper
Recent Thunderbird version stated using gio-launch-desktop helper for opening links, and AppArmor denies that.
Add ix rule to allow running gio-launch-desktop as intermediary for executing browsers.
Fixes https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=908206
Edited by Vincas Dargis