[kfontinst] Port to use icons from the icon theme and make HiDPI aware
Summary:
Use QIcon instead of QPixmap for icons. Use QPushButton for the filter menu instead of a QLabel.
Depends on D23942
Reviewers: Plasma, ngraham
Reviewed By: ngraham
Subscribers: ngraham, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D23868