all: Update application ID to org.gnome.Rhythmbox3
The D-Bus service and the Flathub Flatpak were already using org.gnome.Rhythmbox as the application ID. Rename the appdata, desktop and application icons to match that app-id.
The D-Bus service and the Flathub Flatpak were already using org.gnome.Rhythmbox as the application ID. Rename the appdata, desktop and application icons to match that app-id.