Streamlink Twitch GUI support

https://github.com/streamlink/streamlink-twitch-gui
> A graphical user interface on top of the Streamlink command line interface.
Streamlink Twitch GUI is a NW.js application, which means that it is a web application written in JavaScript (EmberJS), HTML (Handlebars) and CSS (LessCSS) and is being run by a Node.js powered version of Chromium.

tray icons located to **resources.pak**:
https://github.com/streamlink/streamlink-twitch-gui/blob/master/src/config/files.json

aur package instal path: **/opt/streamlink-twitch-gui**
https://aur.archlinux.org/cgit/aur.git/tree/PKGBUILD?h=streamlink-twitch-gui

Start with the referenced src/config/files.json in the Streamlink Twitch GUI repository and inspect the resources.pak tray-icon location. Check the AUR PKGBUILD for the installation path /opt/streamlink-twitch-gui, then compare those details with Hardcode-Tray's existing application support. Done means the GUI's tray icons are correctly identified and handled.

Written by the indexing model from the issue text.