Unify the application id

Currently, GCC uses

org.gnome.ControlCenter per https://gitlab.gnome.org/GNOME/gnome-control-center/blob/master/shell/cc-application.c#L288 org.gnome.Settings per https://gitlab.gnome.org/GNOME/gnome-control-center/blob/master/shell/gnome-control-center.desktop.in.in#L4

The desktop file & the appdata file shipped with GCC still uses gnome-control-center as a name. They should be updated to use the app-id instead.

Was going to prepare a MR to fix that, still not sure which app-id to go with.