Appdata update
This MR:
- Unifies the app-id of the application and uses
org.gnome.lightsoff
for appdata file, desktop file and icons. Other GNOME apps usesorg.gnome.Appname
instead oforg.gnome.appname
but we can keep the later if you prefer. - Updates the appdata to the latest specs
- Add tests to validate the appdata/desktop files.
Next step:
- Add flatpak manifest & set up Gitlab CI for nightly building.