This is a port of the relevant parts of:

Git commit 82e58aa1bf37b7f64ef25b28b85b845b9ff33776 by Friedrich W. H. Kossebau.
Committed on 07/09/2016 at 13:25.
Pushed by kossebau into branch 'master'.

Restore old behaviour: ensure cosmetic pen for UI elements

Qt4 did default to cosmetic pens, Qt5 defaults to 1 pixel pens
Does not make a difference in many places though, but let's be explicit now