Middle-click on QSystemTrayIcon сauses context menu

Summary:
Middle-click on QSystemTrayIcon сauses context menu because inconstant with
http://code.qt.io/cgit/qt/qtbase.git/tree/src/platformsupport/dbustray/qstatusnotifieritemadaptor.cpp?h=5.7#n177
QStatusNotifierItemAdaptor::SecondaryActivate()

BUG: 382855

Reviewers: #plasma, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: cfeck, davidedmundson, McPain

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D7013