Adher to the XDG base directory specification #15

Please use the XDG data dir for data and log dirs.

I just started it and got shown this: {"data-dir":"/home/jfowl/.code-server","working-dir":"/tmp/code-server-dir","log-dir":"/home/jfowl/.code-server/logs/20190305213428008"}. I personally don't like apps to create even more dotfils/dotdirs in my /home directory than it already has. Using the XDG basedir spec would be a great step towards using well-established standards in the unix world <3.