XDG Base Directory Specification support

[tim77]

Hello. Currently ~/.config and ~/.local/share paths are hardcoded in the app. The problem is that non-compliance with the XDG standard doesn't allow to control the location of data/configurations when using environment variables XDG_DATA_HOME/XDG_CONFIG_HOME as prescribed by the specification.

This especially important for packaging app in Flatpak format. This is must have for solving this issue #147.

See:

• https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
• https://doc.qt.io/qt-5/qstandardpaths.html

[brezerk]

Yeah. This is quite good legacy. Looking

[brezerk]

Thanks for reporting; Should be resolved now.

[tim77]

Just awesome. @brezerk thanks a lot. I've already tested a little bit this patches and LGTM.