Application crashes when installed to User Programs. #83
Description
If the application has been installed with sudo python3 setup.py install to user-land programs (/usr), it crashes immediately due to the missing GTK ApplicationWindow default icon. The icon file is looked up only in module local files, or in the snap sandbox.
Additionally, if the GTK HeaderBar icon is not theme-based, then it is assumed to be available in the module local files. Otherwise, when application data has been installed to User Programs, the icon is missing. Apart from the missing icon the application is fully functional, given the former issue has been resolved.