Add style to more plugins in KDE-Plasma theme

[isf63]

• Adds top bar styling to Color Picker, and Status Notifier items

The top bar on Color Picker is not positioned correctly but lxqt/lxqt-panel#2049 corrects that.

[stefonarch]

It looks ok, but for the notification area I'm unsure if we should really change a long standing theme, user might not like a change. Usually icons in notification area have no visible hover effect, expect tooltips ofc.

Afaik @yan12125 uses it, let's here others.

[yan12125]

Thanks for the work. It seems this change brings more benefits (easier to identify the target QToolButton) than issues (additional margin may require reorganizing the panel layout). Overall, I'm fine with this change.

user might not like a change

I'm against a breaking change like #69. This pull request is okay :)

PS. I don't use the color picker. Only status notifiers are tested.

[isf63]

Thanks for reviewing!

I don't use the color picker.

For ColorPicker and Backlight, there exists a bug when panel size is greater than the icon size on several themes, which affects this styling on KDE-Plasma. I mentioned another PR that I think is the fix.