Include existing plugins on non-primary panels

[howels]

When selecting "Display panels on all monitors", the secondary panels on additional monitors are missing other plugins.

For instances, using the quick settings sound device renamer, the devices are only renamed in the primary panel but not others (marcinjahn/gnome-quicksettings-audio-devices-renamer-extension#6).

To make other panels equally functional would assist users with large multi-monitor setups, where returning to the "main" monitor to click some panel item is undesirable.