python/soco: init at 0.15

This is required for one of the plugins (sonosupdate) of Beets version
1.4.7.

I do not have a Sonos speaker, so I can't really test whether the
library works nor properly maintain this package (so I didn't add myself
as a maintainer).

I ran the build (including tests) against Python 2.x and Python 3.x.

Signed-off-by: aszlig <aszlig@nix.build>