Use proper paths for storing user data/config

[rugk]

Ref https://threema-forum.de/thread-2024-post-43299.html#pid43299

In short:

• on Windows something like %AppData%
• for Linux, see here: https://0x46.net/thoughts/2019/02/01/dotfile-madness/, in short $XDG_CONFIG_HOME with a fallback to $HOME/.config
• portable mode (as currently done, so it is usable on an USB etc.), can be enabled via a special text file or so in the app's directory

[blizzard4591]

What files are currently the problem? For the log files, I use QStandardPaths::StandardLocation const location = QStandardPaths::AppLocalDataLocation;

to build the proper path. I hope this works. If not, an error message should be displayed through std::cerr. For the settings, I use the default constructor for QSettings() (https://doc.qt.io/qt-5/qsettings.html) and that seems to imply the NativeFormat, which on Windows is the registry. On my machine, my options are saved under HKEY_CURRENT_USER\Software\openMittsu\OpenMittsu\options. This should not require admin rights.

I will look into this more, but if you have a pointer or ideas what the problem might be, that would be nice.

Also: Is Native/registry not a good choice? Sure, for portable maybe not, but storing them locally next to the binary is even worse for UAC.

[rugk]

Okay, so actually looks good. Just wonder why the forum user had issues then. So probably better discuss/debug this in the forum thread.