Make Briar Desktop work on Windows

The legacy commits can be seen here: https://code.briarproject.org/briar/briar-desktop/-/merge_requests/8/diffs?diff_id=6170&start_sha=79e3e97a0992a7fafdae2b457689f7e5e4e9522c

Depends on briar!1533 (closed).

Closes #31 (closed)