Linux /My Documents/ path listens to XDG_DOCUMENTS_DIR

**Issue**
After setting up the FAF client using the tutorial from [Tatsu](https://www.youtube.com/watch?v=pmH67ZWETO0), I discovered that the documents folder where FAF puts it's downloaded files (maps, mods), is taken from the XDG config which is defined in _~/.config/user-dirs.dirs_

What does this do? Well, if you store your personal documents in a different directory then where you store your Wine documents, you'll not be able to use any mods or downloaded maps. In my case, FAF stored the map in /mnt/userdata/documents and not in /home/documents

You could test this by changing the XDG reference on your machine. I used Ubuntu 18.04 when I discovered this issue.

**workaround**
I made a symlink from the /mnt/userdata folder to the /home/doocuments folder. Alternatively, you could also copy-paste all files, but that gets pretty labour intensive.

**proposed fix**
The most robust way, would be to ask WIne where the /My documents/ are. That way, it will put the files in the same bottle/prefix as where application is started from.

Reproduce the issue on Linux by changing XDG_DOCUMENTS_DIR in ~/.config/user-dirs.dirs and downloading a map or mod. Trace how the FAF client resolves its documents directory, then verify that downloaded files use the Wine prefix's /My Documents/ location rather than the XDG path.

Written by the indexing model from the issue text.