Some differences to the implementation in the current Windows version:
- DirnameUserAppData now points to app dir
- --psettings cli argument is ignored / not supported any longer
- instead, the settings filename is the same as in non-portable mode
(the user may have placed his old portable_settings.txt file here, and we should not overwrite it)
- the user once needs to import his portable_settings.txt after upgrading from pre-v13