improve positioning for highlight in systray
Summary:
--the highlight item used in the systray now uses
the panel thickness for correct positioning. In
the past there were cases that the highlight item
wasnt shown at all or was positioned a bit far from
the panel edge
Test Plan:
use the systray and investigate that highlight item
is positioned correctly
Reviewers: Plasma, mart, davidedmundson
Reviewed By: mart
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D5927