GitLab

change QGuiApplication to QApplication so it uses the correct theme.

I may move this section to a different file later, but for now it's
best to keep all the plasma specific properties together.

X-KDE-PluginInfo-Category list is copied from:
<https://techbase.kde.org/Projects/Plasma/PIG>

X-Plasma-Provides, X-Plasma-NotificationArea and
X-Plasma-DBusActivationService code blurbs are from:
https://community.kde.org/Plasma/DeveloperGuide#Provides_.28Alternatives.29

Link devicePixelRatio to the API docs.

Make the wording a bit more concise