Make a self-contained MacOS zip-package for easy install on end-user machines

A bash script, setup_scripts/mk_macos_pkg.sh, is added to make a simple self-contained MacOS package in zip format.

Hence the end-user needs only to uncompress the package via unzip and run the application.

The package includes all the required libraries, excluding the Qt dependencies. Including the Qt dependencies, albeit possible, is cumbersome and dramatically increases the size of the package. Furthermore, installing the required Qt dependencies is very simple,
via Homebrew

brew install qt@5

or MacPorts

port install qt5

A debugging bash script, setup_scripts/dbg_macos_pkg.sh, is also added to gather relevant information about the end-user machine, in case the application execution fails.

The GitLab CI script is modified to make and store the MacOS zip-package as an artifact. The previous dysfunctional CPack package is commented out.