Port applets to use PlasmaExtras.PlaceholderMessage
The Kirigami version uses QQC2 elements which don't respect the plasma theme and color scheme, leading to thing slooking out of place especially when using a dark color theme or scheme.
Depends on https://invent.kde.org/frameworks/plasma-framework/-/merge_requests/13
Please do not squash when merging.
Edited by Nate Graham