Set prgname to match the application id

[bbhtt]

When launched on wayland with WAYLAND_DEBUG=1 Liferea sets the app id "liferea" but not net.sourceforge.liferea:

[1225601.077]  -> xdg_toplevel@41.set_app_id("liferea")

When launched on KDE Wayland session, it expects the desktop file name to match the application id to look up the correct app icon to show in taskbar app switcher etc. But instead it tries too look up an icon called "liferea" which does not exist. So liferea shows up with the default wayland icon instead of the app icon.

Setting WM_CLASS here won't work and we can't export two desktop files.

This does not effect GNOME because it tries harder to guess the app icon.

[bbhtt]

I think this was overlooked when everything was changed to match the app id in https://github.com/lwindolf/liferea/commit/0dea39b79802588ebe60aadbd8e54ea02c9b7720

But actually the appid was liferea all this time.

I myself didn't notice this because I don't use KDE. But happened to see it when debugging the tray icon issue with flatpaks and testing it on KDE.

This should not cause any change in behavior other than just setting the "correct" app id:

[1643363.357]  -> xdg_toplevel@37.set_app_id("net.sourceforge.liferea")

The icons and desktop file are already named net.sourceforge.liferea so nothing else needs to change.

[bbhtt]

You can check the desktopFilename KDE plasma wayland expects by running qdbus org.kde.KWin /KWin org.kde.KWin.showDebugConsole > Wayland windows > Liferea