What is the minimum version of QT required?

[u-235]

Hi.

I tried to build an application with Qt version 5.12.8 and got errors "'textActivated' is not a member of 'QComboBox'" for files alphaplot/src/PlotWizard.cpp and alphaplot/src/analysis/FFTDialog.cpp. The QComboBox::textActivated signal is available from Qt version 5.14, but the "INSTALL.md" specifies a minimum version of 4.3. Of course, the days of Qt4 are long gone, but version 5.12 is still relevant.

The changes that break the build were made in the e6d475d commit.