Use feature_summary
Make PAM package REQUIRED in case of build with PAM
Set proper AUTOMOC options when building Qt5 version
Port away from qt5_use_modules to imported targets; clean target_link_libs
Find all needed Qt5 packages
Make moc work for PAM.cpp by explicitely passing the USE_PAM definition

Otherwise it fails to link as the moc generates empty file.
Qt5 no more has QString::toAscii(), replace it with ::toLatin1()