Fix huge icons with vertical panel

There was a conflict between adding a config option [1] in master and a
fix to crop to the icon size [2] in the 5.7 branch. I still need the
cropping on my vertical panel, otherwise the icons are insanely big.

[1] https://git.reviewboard.kde.org/r/128400/
[2] https://phabricator.kde.org/D2160

Reviewed-By-Over-IRC: Marco Martin <notmart@gmail.com>
BUG: 365394