Performing a dev build against the latest version of Qt failed
because of some deprecated members. They have been replaced
according to the Qt documentation.
Further, Q_OS_MACOS is now the only macro available to identify a
machine running macOS, the others are now deprecated.
See https://doc.qt.io/qt-5/qtglobal.html#Q_OS_OSX and
https://doc.qt.io/qt-5/qtglobal.html#Q_OS_MAC.
This enables coordinate system scaling for high-DPI
displays, which enforces correct proportions even
on small 4k displays. The icons are scaled up without
interpolation, which makes them crisp, but a bit
pixelated. A new scalable icon set will solve this
problem, but is not scope of this patch.
Resolves#548, #1381, #1710, #1888
In addition, this patch enforces the KeePassXC icon
theme for the KMessageBox close icon, since using
the system theme produces very ugly icons on some
Linux systems.
KeepassXC tries to load the theme icon first and then falls back to the internal icon unless the check is explicitely disabled. Remove the check from most icons
Fixes#756
