applet: Replace usages of plasmoid.rootItem
Referencing plasmoid.rootItem
no longer works with the new Plasmoid API
so their usages on list items are failing.
BUG: 470850 FIXED-IN: 6
This fixes the issues with many behaviours on the list items (context menu, dragging, ...) which work again as usual. But referencing an external item by its id is not usually recommended, so there is probably a better way, or maybe some API can be added for this use case.
So marking as draft and waiting for @mart's opinion.